Revert "Metal: add loadMSAAFromResolve support."

This reverts commit 9f82158f17ee638e11cf68cbb07d0cec1a4c847c.

Reason for revert: broke Flutter/iOS

Original change's description:
> Metal: add loadMSAAFromResolve support.
>
> Also fixes some minor warnings.
>
> Bug: skia:12086
> Change-Id: Ia476a7a196b490022978761e92f935a6d668136a
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/441797
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Jim Van Verth <jvanverth@google.com>

TBR=egdaniel@google.com,jvanverth@google.com,skcq-be@skia-corp.google.com.iam.gserviceaccount.com

Change-Id: I82ce91628a0921bcf8dd831ded0bb83937f5cadb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:12086
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/445637
Commit-Queue: Florin Malita <fmalita@google.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Florin Malita <fmalita@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
7 files changed