Revert "Add the full set of linux_chromeos_gtests to the internal linux-chromeos-rel bot."

This reverts commit 1687ec2e.

Reason for revert: bot's aren't ready yet

See crbug.com/932269#c21

Original change's description:
> Add the full set of linux_chromeos_gtests to the internal linux-chromeos-rel bot.
>
> There may not be enough linux swarming bots in chrome-swarming to run the
> tests. I can throw some in there if needed.
>
> # NOTRY=true
>
> Bug: 932269, 875593
> Change-Id: I336c4e159b12d56d178681548af92e5fec767a17
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1532501
> Commit-Queue: Ben Pastene <bpastene@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#643084}

TBR=dpranke@chromium.org,bpastene@chromium.org,jbudorick@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 932269, 875593
Change-Id: Ib3bde5a99af0da045680f3b744048c0c28734017
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1536811
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644107}

testing/buildbot/mixins.pyl

@@ -160,9 +160,6 @@
   'code-coverage': {
     'isolate_coverage_data': True,
   },
-  'experimental': {
-    'experiment_percentage' : 100,
-  },
   'flounder': {
     # Nexus 9
     'swarming': {

testing/buildbot/waterfalls.pyl

@@ -623,12 +623,6 @@
           'chrome',
         ],
       },
-      'linux-chromeos-google-rel': {
-        'mixins': ['experimental'],
-        'test_suites': {
-          'gtest_tests': 'linux_chromeos_gtests',
-        },
-      },
     },
   },
   {