Remove RenderEmbeddedObject::layerTypeRequired().

This method does not seem to do anything useful. It overrides
RenderPart::layerTypeRequired(), which does exactly the same thing.

Review URL: https://codereview.chromium.org/309763002

git-svn-id: svn://svn.chromium.org/blink/trunk@175297 bbb929c8-8fbe-4397-9dbb-9b2b20218538