DevTools: Remove orphaned CSS rules [7]

These rules seem to be never applied.

BUG=
NOTRY=true

Review URL: https://codereview.chromium.org/432783002

git-svn-id: svn://svn.chromium.org/blink/trunk@179376 bbb929c8-8fbe-4397-9dbb-9b2b20218538