This reverts commit 1e4f8b02.

Reason for revert:
Earlier CL breaks pre-rotation:
https://chromium-review.googlesource.com/c/angle/angle/+/2598584

Original change's description:
> Vulkan: Generate gl_Position.z correction in SPIR-V
>
> Instead of having the translator output code to transform gl_Position.z
> to Vulkan clip space in the vertex stage, this change makes the SPIR-V
> transformer perform this operation on the last geometry stage.
>
> An alternative solution would be to generate this transformation in the
> translator in every geometry stage, each controlled by a separate
> specialization constant.  This change avoids unnecessary modifications
> to earlier stages.  Additionally, the transformer is already modifying
> gl_Position.xy for pre-rotation, so the addition of a small
> transformation of gl_Position.z in the same spot is rather trivial.
>
> Bug: angleproject:5479
> Change-Id: Id971179ba47b206204bfdaf3b2b295ef97dd5117
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2598585
> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
> Reviewed-by: Charlie Lao <cclao@google.com>
> Reviewed-by: Jamie Madill <jmadill@chromium.org>

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

Change-Id: I3bdf3d6f743125eaf552608f2664b715bd6935c5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:5479
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2634203Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Tim Van Patten <timvp@google.com>