REGRESSION (r218228): Layout Test editing/execCommand/strikethrough-uses-strike-tag...

REGRESSION (r218228): Layout Test editing/execCommand/strikethrough-uses-strike-tag.html is failing
https://bugs.webkit.org/show_bug.cgi?id=173375

Unreviewed test gardening.

Reverted an incorrect baseline and skipped a test causing test failures.

* TestExpectations:
* platform/mac-wk1/editing/execCommand/strikethrough-uses-strike-tag-expected.txt: Removed.
* platform/win/editing/execCommand/strikethrough-uses-strike-tag-expected.txt: Removed.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@218346 268f45cc-cd09-0410-ab3c-d52691b4dbfc