Color attachment output ordering applies to commands recorded within a
render pass subpass.  We still need execution barriers between render
passes (and subpasses, but we don't use them).

Bug: angleproject:3347
Change-Id: Ifaddaeac35347d8a35e771f46a29047d52c9541c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1713085Reviewed-by: Fei Yang <fei.yang@arm.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>