Remove duplicated "display: flow-root" test

The test for "display: flow-root" has been upstreamed
into W3C csswg-test repository.

With the last import of csswg-test in r446595
the test is now duplicated.

This patch removes it from fast/block/float/.

BUG=672508

Review-Url: https://codereview.chromium.org/2655223004
Cr-Commit-Position: refs/heads/master@{#446721}
3 files changed