Remove dead code in RenderLayerCompositor.h

The method implementation does not exist, and the functionality now lives in |CompositingRequirementsUpdater|.

BUG=None

Review URL: https://codereview.chromium.org/522173005

git-svn-id: svn://svn.chromium.org/blink/trunk@181254 bbb929c8-8fbe-4397-9dbb-9b2b20218538