Revert of Convert compositor_unittests to run exclusively on Swarming

testing/buildbot/chromium.webkit.json

 {
   "Linux ChromiumOS Tests (1)": {
     "gtest_tests": [
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "accessibility_unittests"
       },
       {
@@ skipping 48 matching lines @@
       {
         "test": "chromevox_tests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "components_unittests"
       },
       {
-        "swarming": {
-          "can_use_on_swarming_builders": true
-        },
         "test": "compositor_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "content_browsertests"
       },
       {
         "swarming": {
@@ skipping 234 matching lines @@
         },
         "test": "chromeos_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "components_unittests"
       },
       {
-        "swarming": {
-          "can_use_on_swarming_builders": true
-        },
         "test": "compositor_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true,
           "shards": 2
         },
         "test": "content_browsertests"
       },
       {
@@ skipping 869 matching lines @@
         "name": "webkit_lint",
         "script": "webkit_lint.py"
       },
       {
         "name": "webkit_python_tests",
         "script": "webkit_python_tests.py"
       }
     ]
   }
 }