Revert "Mark window-resize-{percent-width-height,child-background-image-fixed-centered}.html flaky on Win"

This reverts commit d4763bd6fa6deddafbb964d93ea5f5df5cc09791.

Reason for revert: Seems only temporary flakiness on one bot.
Remove the flakiness entry to ensure test coverage.

Original change's description:
> Mark window-resize-{percent-width-height,child-background-image-fixed-centered}.html flaky on Win
> 
> TBR=wangxianzhu@chromium.org
> 
> Bug: 945666
> Change-Id: Ifbf20c92ebb0bf5038fab76d7c4f98121fa63746
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539217
> Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#644191}

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

Change-Id: I1d2e62f2cb31a0d71d8c7d2a19cccbb2fd2a33f5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 945666
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1537647
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644199}
1 file changed