[Telemetry] Clean up outdated reason for disabling system_health.common_desktop story.

TBR=charliea@chromium.org,nednguyen@google.com

Change-Id: Iae8eef1ccdbf192ffac79cfd3f4ef80ba249f7d0
Reviewed-on: https://chromium-review.googlesource.com/728351Reviewed-by: rnephew <rnephew@chromium.org>
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: rnephew <rnephew@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510183}

tools/perf/page_sets/system_health/expectations.py

@@ -9,9 +9,8 @@ class SystemHealthDesktopCommonExpectations(expectations.StoryExpectations):
     self.DisableStory('browse:news:hackernews',
                       [expectations.ALL_WIN, expectations.ALL_MAC],
                       'crbug.com/676336')
-    self.DisableStory('browse:search:google',
-                      [expectations.ALL_WIN],
-                      'win:crbug.com/673775, mac:crbug.com/756027')
+    self.DisableStory('browse:search:google', [expectations.ALL_WIN],
+                      'crbug.com/673775')
     self.DisableStory('play:media:google_play_music', [expectations.ALL],
                       'crbug.com/649392')
     self.DisableStory('play:media:soundcloud', [expectations.ALL_WIN],