testing/buildbot: Disable tests on ToTAndroid x64

There are currently no devices available to run the tests, so the bot
has been red for a long time.

Disable the tests for now to make the bot green and ensure we don't
regress being able to compile this config.

Bug: 807966
Change-Id: I93442e6511a5c8c4e4a38346b1510b233743f593
Reviewed-on: https://chromium-review.googlesource.com/898983
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534038}

testing/buildbot/waterfalls.pyl

@@ -669,7 +669,7 @@
           ],
         },
         'test_suites': {
-          'gtest_tests': 'chromium_android_clang_and_gl_gtests',
+          # TODO(crbug.com/807966): Re-enable tests once there are devices to run them on.
         },
       },
       'ToTAndroid64': {