Revert "implement SkPixmap::erase() with draws"

This reverts commit 42f29f11817f9829b92dbf52d77f1447fbfc5ed0.

Reason for revert: Chrome roll?

Original change's description:
> implement SkPixmap::erase() with draws
> 
> I don't want to have to maintain yet another switch on SkColorType.
> 
> This should also make color management a bit clearer?
> 
> Change-Id: I1508e0c30670b1987972f7eeba2dd6d23591c531
> Reviewed-on: https://skia-review.googlesource.com/154862
> Commit-Queue: Mike Klein <mtklein@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>

TBR=mtklein@google.com,brianosman@google.com

Change-Id: Ic05f49db7c3dd2c73a53622411e7f8d0f90773a9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/155161
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed