WebUI: Remove unused --settings-checkbox-label mixin

The mixin got removed during MD refresh and adding it back seems to make
it looks worse than it currently does

Bug: 973674
Change-Id: I561c41b5d3a204823db1578902a11e0a6f0cd42e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674453
Reviewed-by: Esmael El-Moslimany <aee@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672162}
1 file changed