Re-enable media/media-ended.html

This test was marked as flaky, but it has not failed
in a while so we should try and re-enable it.

BUG=874500

Change-Id: I7564d54a82af721a72fb4e1b2fb836415edd5c07
Reviewed-on: https://chromium-review.googlesource.com/c/1354620Reviewed-by: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612256}

third_party/blink/web_tests/TestExpectations

@@ -4485,7 +4485,6 @@ crbug.com/722943 virtual/video-surface-layer/media/audio-repaint.html [ Skip ]
 crbug.com/873454 css3/filters/effect-reference-image-hw.html [ Failure Pass ]
 
 # Sheriff failures 2018-08-15
-crbug.com/874500 [ Mac ] media/media-ended.html [ Pass Timeout ]
 crbug.com/874567 [ Mac ] svg/custom/getscreenctm-in-scrollable-div-area-nested.xhtml [ Pass Failure ]
 crbug.com/874837 [ Win ] ietestcenter/css3/bordersbackgrounds/background-attachment-local-scrolling.htm [ Pass Failure ]
 crbug.com/874866 [ Mac ] virtual/new-remote-playback-pipeline/media/controls/modern/doubletap-to-jump-backwards-at-start.html [ Pass Timeout ]