Temporarily remove telemetry_unitests from chromeos-kevin-rel.

Until crbug.com/1141234 is complete, the current public kevin pool
is quite overloaded. eg:
https://ci.chromium.org/p/chromium/builders/try/chromeos-kevin-rel/3153?
https://ci.chromium.org/p/chromium/builders/try/chromeos-kevin-rel/3158?

This should help reduce load while we wait for more DUT capacity.

Bug: None
Change-Id: I468eca706b709121e4267f411a1ab57b5c9cb4dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2570072Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833049}

testing/buildbot/chromium.chromiumos.json

@@ -1248,39 +1248,6 @@
         "trigger_script": {
           "script": "//testing/trigger_scripts/chromeos_device_trigger.py"
         }
-      },
-      {
-        "args": [
-          "--browser=cros-chrome",
-          "--remote=variable_chromeos_device_hostname",
-          "--jobs=1"
-        ],
-        "isolate_name": "telemetry_unittests",
-        "merge": {
-          "args": [],
-          "script": "//testing/merge_scripts/standard_isolated_script_merge.py"
-        },
-        "name": "telemetry_unittests",
-        "resultdb": {
-          "enable": true
-        },
-        "swarming": {
-          "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "device_type": "kevin",
-              "os": "ChromeOS",
-              "pool": "chromium.tests"
-            }
-          ],
-          "idempotent": false,
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 10
-        },
-        "test_id_prefix": "ninja://chrome/test:telemetry_unittests/",
-        "trigger_script": {
-          "script": "//testing/trigger_scripts/chromeos_device_trigger.py"
-        }
       }
     ]
   },

testing/buildbot/test_suite_exceptions.pyl

@@ -2692,6 +2692,8 @@
       },
     },
     'remove_from': [
+      'chromeos-kevin-rel',  # crbug.com/1141234: Restore when there's more DUTs
+
       # crbug.com/936540
       'Mac10.11 Tests',