Revert "Increase specificity of GrColorType computed for YUV planes"

This reverts commit c326aaf134f4ee8067bbe41742580307dd4d5a72.

Reason for revert: ANGLE D3D es2 bots

Original change's description:
> Increase specificity of GrColorType computed for YUV planes
> 
> When a single channel texture is used for a YUV channel we will
> interpret it as kGray_8. When a single channel texture is used
> as an A channel we will interpret it as kAlpha_8.
> 
> Change-Id: I746f8d761d7779266a4106311a93d651266bb422
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/232017
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>

TBR=bsalomon@google.com,robertphillips@google.com

Change-Id: I57a00d65c6226822a501b231e103016a45943e5e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/232138
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
13 files changed