[selectors4] Remove :focus-within test that is now duplicated

This patch removes the following test:
  fast/selectors/focus-within-display-none.html

The test was upstreamed into the WPT repository and it's imported as:
  external/wpt/css/selectors4/focus-within-display-none-001.html

The new test includes the old checks and some more, so we don't need
our own test anymore.

BUG=617371

Review-Url: https://codereview.chromium.org/2862013002
Cr-Commit-Position: refs/heads/master@{#469610}
2 files changed