Removing unused render target format in D3D11 This takes up about 2.9% of the time in performance runs. BUG=angleproject:1161 Change-Id: I9ff98cd6f4bfd14cab0c702d5873f3fadfbcb4d7 Reviewed-on: https://chromium-review.googlesource.com/317574 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tryjob-Request: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Dian Xiang <dianx@google.com>