Remove applyAuthorStyles machinery from ShadowRoot and ElementShadow

We don't support setting applyAuthorStyles anymore, so we don't need
any of this logic. I left the stuff in the resolver since that requires
bigger changes.

Review URL: https://codereview.chromium.org/227383003

git-svn-id: svn://svn.chromium.org/blink/trunk@171090 bbb929c8-8fbe-4397-9dbb-9b2b20218538