Revert "[mac-rel-swarming] add arm-64 Mac to the target bots"

This reverts commit 93873650.

Reason for revert: The mixin isn't necessary anymore.
Ignore-CQ-Freeze: true

Original change's description:
> [mac-rel-swarming] add arm-64 Mac to the target bots
>
> ARM Mac bots have 'arm64' cpu dimension.
> https://chromium-swarm-dev.appspot.com/bot?id=build201-a9
>
> Adding Ignore-CQ-Freeze because this isn't for production.
>
> Ignore-CQ-Freeze: true
> Bug: 1103470
> Change-Id: I3d3713909994a88224aec6c9eaf48e9d0890d2ab
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2320714
> Commit-Queue: Junji Watanabe <jwata@google.com>
> Reviewed-by: Ben Pastene <bpastene@chromium.org>
> Reviewed-by: Erik Staab <estaab@chromium.org>
> Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
> Auto-Submit: Junji Watanabe <jwata@google.com>
> Cr-Commit-Position: refs/heads/master@{#792461}

TBR=estaab@chromium.org,martiniss@chromium.org,tikuta@chromium.org,bpastene@chromium.org,jwata@google.com,yekuang@google.com

Change-Id: Ic96fb6dbb7934065cffeb637c132d23ff3202c0f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1103470
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2325452
Auto-Submit: Junji Watanabe <jwata@google.com>
Reviewed-by: Erik Staab <estaab@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Erik Staab <estaab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792543}

testing/buildbot/chrome.ci.json

@@ -3799,11 +3799,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "base_unittests",
@@ -3816,11 +3811,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "content_browsertests",
@@ -3833,11 +3823,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "content_unittests",
@@ -3850,11 +3835,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "interactive_ui_tests",
@@ -3867,11 +3847,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "net_unittests",
@@ -3884,11 +3859,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "unit_tests",

testing/buildbot/chromium.dev.json

@@ -902,11 +902,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "base_unittests",
@@ -919,11 +914,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "content_browsertests",
@@ -936,11 +926,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "content_unittests",
@@ -953,11 +938,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "interactive_ui_tests",
@@ -970,11 +950,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "net_unittests",
@@ -987,11 +962,6 @@
         },
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "cpu": "x86-64|arm64"
-            }
-          ],
           "service_account": "chromium-tester-dev@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "unit_tests",

testing/buildbot/mixins.pyl

@@ -481,13 +481,6 @@
       },
     },
   },
-  'mac_all_arch': {
-    'swarming': {
-      'dimensions': {
-        'cpu': 'x86-64|arm64',
-      },
-    },
-  },
   'mac_mini_10.12': {
     'swarming': {
       'dimensions': {

testing/buildbot/waterfalls.pyl

@@ -1659,9 +1659,6 @@
         },
       },
       'mac-rel-swarming': {
-        'mixins': [
-          'mac_all_arch',
-        ],
         'test_suites': {
            'gtest_tests': 'chromium_swarm_desktop_gtests',
         },