DevTools: Remove orphaned CSS rules [3]

See https://bugs.webkit.org/show_bug.cgi?id=72920

BUG=
NOTRY=true

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179311

Review URL: https://codereview.chromium.org/438603002

git-svn-id: svn://svn.chromium.org/blink/trunk@179390 bbb929c8-8fbe-4397-9dbb-9b2b20218538