Simplify bitmappremul GM a bit, remove more SkColorData 4444 macros

Bug: skia:
Change-Id: I294e70708aab2c39a6077a11de76518c6fe7f712
Reviewed-on: https://skia-review.googlesource.com/c/167941
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
2 files changed