There was already a changeLayout call that inserted an imageBarrier.  A
TRANSFER_SRC to TRANSFER_SRC barrier was unnecessarily (and manually)
added afterwards that was pointless.

Bug: angleproject:3816
Change-Id: I8177487fc843fa5869c7b5063c74602933a81d58
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1929270Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Sunny Sun <sunny.sun@arm.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>