FramebufferD3D: Only make sure that enabled attachments are not the same. It's acceptable to have the same object attached to muliple framebuffer attachments if they are not being drawn to. This was triggering failures in the conformance2/state/gl-object-get-calls.html test. BUG=483282 Change-Id: If088ccd9b1189f060dfa33ebbe4d82f1f47559b0 Reviewed-on: https://chromium-review.googlesource.com/354570 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>