This reverts commit b1917fe1.

Reason for revert: Not the root cause. See bug.

Original change's description:
> Revert "Vulkan: Use specialization constant for halfRenderAreaWidth"
>
> This reverts commit ff38106d.
>
> Reason for revert: Speculative revert to clear up AMD. See bug.
>
> Bug: chromium:1154356
>
> 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
>
> Change-Id: Idab612bcad4f179857c41ffc4bf8fa2355fae946
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: b/173800146
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2568244
> Reviewed-by: Jamie Madill <jmadill@chromium.org>
> Commit-Queue: Jamie Madill <jmadill@chromium.org>

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

# Not skipping CQ checks because this is a reland.

Bug: chromium:1154356
Bug: b/173800146
Change-Id: I5b86bbee8600c6597620f31d8d7b08ca8b3d2d57
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2568246Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>