This reverts commit ff38106d.

Reason for revert: Suspect that this CL may be causing win-angle-rel-32 bot failures

Original change's description:
> Vulkan: Use specialization constant for halfRenderAreaWidth
>
> halfRenderArea is used by fragment shader to adjust gl_FragCoord for
> rotation and yflip compensation. This CL bakes halfRenderAreaWidth into
> shader via specialization constant, thus allow compiler to consolidate
> the calculation into one MAD instruction.
>
> Bug: b/173800146
> Change-Id: Id66301278e3389e2582369b695825e632bccecee
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2551541
> Commit-Queue: Charlie Lao <cclao@google.com>
> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
> Reviewed-by: Tim Van Patten <timvp@google.com>
> Reviewed-by: Jamie Madill <jmadill@chromium.org>

TBR=timvp@google.com,syoussefi@chromium.org,jmadill@chromium.org,cclao@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: b/173800146
Change-Id: I7bc9966ebbe949f3999d7927afa629dd2e3a4187
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2572801Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Ian Elliott <ianelliott@google.com>