Revert of Convert compositor_unittests to run exclusively on Swarming (patchset #6 id:100001 of https://codereview.chromium.org/1211053005/)

Reason for revert:
Causing steps exception compositor_unittests on Linux ChromiumOS Tests (dbg)(1)
Link: https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%28dbg%29%281%29/builds/4229

Shard https://chromium-swarm.appspot.com/user/task/286f8616fee52710 says

Outputs:
Output:
Sending the crash report ... done.
Report URL: https://isolateserver.appspot.com/restricted/ereporter2/errors/5669961011822592
IsolatedFile a8902feeee5e075f3f92ec6ae3299106595667a3 is retrieved recursively

Original issue's description:
> Convert compositor_unittests to run exclusively on Swarming
>
> 0 configs already ran on Swarming
> 18 used to run locally and were converted:
> - chromium.chromiumos.json: Linux ChromiumOS Tests (1)
> - chromium.chromiumos.json: Linux ChromiumOS Tests (dbg)(1)
> - chromium.fyi.json: ClangToTLinux tester
> - chromium.fyi.json: Linux Trusty
> - chromium.fyi.json: Linux Trusty (dbg)
> - chromium.linux.json: Linux Tests
> - chromium.linux.json: Linux Tests (dbg)(1)
> - chromium.linux.json: Linux Tests (dbg)(1)(32)
> - chromium.memory.fyi.json: Linux ChromeOS MSan Tests
> - chromium.memory.fyi.json: Linux MSan Tests
> - chromium.memory.json: Linux Chromium OS ASan LSan Tests (1)
> - chromium.webkit.json: Linux ChromiumOS Tests (1)
> - chromium.webkit.json: Linux ChromiumOS Tests (dbg)(1)
> - chromium.win.json: Vista Tests (1)
> - chromium.win.json: Win 7 Tests x64 (1)
> - chromium.win.json: Win7 Tests (1)
> - chromium.win.json: Win7 Tests (dbg)(1)
> - chromium.win.json: XP Tests (1)
>
> Ran:
>   ./manage.py --convert compositor_unittests
>
> BUG=98637
>
> Committed: https://crrev.com/db1d33845c8847693ab97db88fbcff754c6b3a5b
> Cr-Commit-Position: refs/heads/master@{#337334}

TBR=danakj@chromium.org,maruel@chromium.org,thakis@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=98637

Review URL: https://codereview.chromium.org/1214063007

Cr-Original-Commit-Position: refs/heads/master@{#337352}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d903850ee3b13ee59aadea96cea7e52f0d4bd8c4

gn_migration.gypi

@@ -546,7 +546,6 @@
             '../tools/gn/gn.gyp:gn_unittests_run',
             '../ui/accessibility/accessibility.gyp:accessibility_unittests_run',
             '../ui/app_list/app_list.gyp:app_list_unittests_run',
-            '../ui/compositor/compositor.gyp:compositor_unittests_run',
             '../ui/events/events.gyp:events_unittests_run',
             '../ui/gl/gl_tests.gyp:gl_unittests_run',
             '../ui/message_center/message_center.gyp:message_center_unittests_run',