Remove unused setAlphaAndRequiredFrame condition

Also add some commentary.

Bug: skia:
Change-Id: I164c4004802387981b76b28adc106ac0e65fc3ce
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/196820
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
2 files changed