This reverts commit 0f86b196.

Reason for revert:
Breaks pre-rotation for all apps, so they are displayed in portrait instead of landscape.

Original change's description:
> Vulkan: Generate gl_Position pre-rotation in SPIR-V
>
> Instead of having the translator output pre-rotation code in the vertex
> stage based on a specialization constant, this change makes the SPIR-V
> transformer perform pre-rotation of gl_Position on the last geometry
> stage.
>
> An alternative solution would be to generate pre-rotation code in the
> translator in every geometry stage, each controlled by a separate
> specialization constant.  This change avoids unnecessary modifications
> to earlier stages.  The generated shaders are also smaller, as they
> don't contain a mat2[8] pre-rotation constant matrix.  The SPIR-V
> transformer knows the pre-rotation at transformation time, so it can
> simply use swizzles to achieve the same results.
>
> This also ties in with upcoming changes which move gl_Position.z
> correction to the last geometry shader stage, which is trivially done
> piggy-backing on the infrastructure in this change.
>
> Bug: angleproject:5478
> Change-Id: I9d5d9d19f3ccda665f5504368ce5ddfa5f383faf
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2598584
> 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: I81f237fa6b10c7d59831363bee8999e7ad2f09be
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:5478
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2633694Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Tim Van Patten <timvp@google.com>