Metal: Stop pre-creating the Provoking Vertex CmdBuffer The provoking vertex command buffer was being created regardless if whether or not it was used which is left over from when the backend used to pre-enqueue command buffers. That's no longer true so we don't need to pre-create this command buffer. I think this adds a 5% perf increase to the MotionMark "Leaves" test. Bug: angleproject:7619 Change-Id: Ic921911eeef0f063ea6eba8ba7c307157243b938 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3863739 Reviewed-by: Kenneth Russell <kbr@chromium.org> Commit-Queue: Gregg Tavares <gman@chromium.org>