With the new shared state structure, we can eliminate a lot of the
state tracking within the FramebufferD3D implementation.

BUG=angleproject:930

Change-Id: I0953e321bae3afe7cde7b73c55af62546665c890
Reviewed-on: https://chromium-review.googlesource.com/254101Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>