RenderLayerScrollableArea shouldn't call updateLayerCompositingState

Conceptually, there's no reason for RenderLayerScrollableArea to call
updateLayerCompositingState and no tests fail when the call is removed.

BUG=343756,336251

Review URL: https://codereview.chromium.org/321283003

git-svn-id: svn://svn.chromium.org/blink/trunk@175937 bbb929c8-8fbe-4397-9dbb-9b2b20218538