Revert "Vulkan:Include precision qualifier in GLSL"

This reverts commit 93e72f5f0eb80b89334ea8fe577b32901a00b5fb.

Reason for revert: This is having a negative impact on gfxbench
Manhattan 3.1 tests (20-30%) with only a minor improvement (~4%) in TRex offscreen. Pulling out for now and need to re-evaluate best
solution here.

Original change's description:
> Vulkan:Include precision qualifier in GLSL
> 
> With this initial implementation, it's possible to get precision
> qualifier mis-matches in the generated GLSL 4.50. According to the
> spec this is allowed. From GLSLangSpec 4.50 section 4.7 "Precision and
> Precision Qualifiers":
> 
> For the purposes of determining if an output from one shader stage
> matches an input of the next stage, the precision qualifier need not
> match.
> 
> However, when converted to SPIR-V and run through the shader validation
> any mismatches will cause shader validation errors. Initially just
> ignoring those errors with this commit.
> 
> Bug: angleproject:3078
> Change-Id: Ia2b04f90f0a7b6b1302c1b1b3e32bcfd8db9ed49
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2057749
> Reviewed-by: Jamie Madill <jmadill@chromium.org>
> Reviewed-by: Tobin Ehlis <tobine@google.com>
> Reviewed-by: Tim Van Patten <timvp@google.com>
> Commit-Queue: Tobin Ehlis <tobine@google.com>

TBR=tobine@google.com,timvp@google.com,jmadill@chromium.org

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

Bug: angleproject:3078
Change-Id: I84984e2a963bde573f0f1de585001ceb83623c89
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2079334
Reviewed-by: Tobin Ehlis <tobine@google.com>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>