Revert "[webkit] Mark composited-with-hit-testing.html as flaky"

This reverts commit ab595088.

Reason for revert: With https://chromium.googlesource.com/chromium/src/+/c838bf406fc8f97bd8c26a713f80e7290c1f39d3 reverted, this is no longer broken or flaky.

Original change's description:
> [webkit] Mark composited-with-hit-testing.html as flaky
> 
> TBR=wangxianzhu
> 
> Bug: 819591
> Change-Id: I5580ac037f5d6634a5d76708a0ff8c7dbd73c53a
> Reviewed-on: https://chromium-review.googlesource.com/951788
> Reviewed-by: Jan Wilken Dörrie <jdoerrie@chromium.org>
> Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#541413}

TBR=wangxianzhu@chromium.org,jdoerrie@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 819591
Change-Id: I47f361c527f7e29e7c4b88ec2207704e026fcc8b
Reviewed-on: https://chromium-review.googlesource.com/962821
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544105}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3374,5 +3374,4 @@ crbug.com/681919 [ Linux Debug ] http/tests/media/media-src-suspend-after-have-m
 crbug.com/681919 [ Linux Debug ] http/tests/media/media-src-suspend-before-have-metadata.html [ Timeout Pass ]
 
 # Sheriff 2018-03-07
-crbug.com/819591 virtual/threaded/animations/hit-testing/composited-with-hit-testing.html [ Failure Pass ]
 crbug.com/819778 [ Linux ] external/wpt/css/cssom-view/interfaces.html [ Pass Timeout ]