Remove no-op did(De)activateCompositor calls

These have been removed in Chrome and do nothing.

R=jochen@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/298803009

git-svn-id: svn://svn.chromium.org/blink/trunk@175725 bbb929c8-8fbe-4397-9dbb-9b2b20218538