Remove some unneeded colortype format validation checks in ProxyProvider.

These checks are no longer needed as we have enough checks in other parts
of the code now. Additionally we want to remove any GrColorType and format
compatibility checks in proxy provider since proxies will not have knowledge
of color types in the future.

This also lets us get ride of some used of GrPixelConfig.

Change-Id: Ice835cba69ff783fd7e7d9b57321882b1e50093a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248803
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed