Remove pixel write/read tests.

I found myself updating these for another change and realized they
are very limited tests that are redundant with more thorough tests.

Change-Id: I935da4d1da7ff3825a4042556845a8eb659b6ba8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/346856
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Auto-Submit: Brian Salomon <bsalomon@google.com>
9 files changed