Cleanup generate_buildbot_json.py

Reference: https://chromium-review.googlesource.com/c/chromium/tools/build/+/2472980

Bug: 1024915
Change-Id: I88fea2732cfca7f99c658beeb87c562de07518fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2476694
Auto-Submit: Prakhar Asthana <pasthana@google.com>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Prakhar Asthana <pasthana@google.com>
Cr-Commit-Position: refs/heads/master@{#817567}

testing/buildbot/generate_buildbot_json.py

@@ -1430,13 +1430,6 @@ class BBJSONGenerator(object):
         'Win x64 Builder Code Coverage',
         'Win10 Tests x64 Code Coverage',
         'Win10 x64 Release (NVIDIA) Code Coverage',
-        # TODO(crbug.com/1024915) Delete these when coverage is enabled by
-        # default on Mac OS tryjobs.
-        'Mac Builder Code Coverage',
-        'Mac10.13 Tests Code Coverage',
-        'GPU Mac Builder Code Coverage',
-        'Mac Release (Intel) Code Coverage',
-        'Mac Retina Release (AMD) Code Coverage',
     ]
 
   def get_internal_waterfalls(self):