Revert of add readPixels() to SkBitmap (https://codereview.chromium.org/377303002/)

Reason for revert:
Maybe causing crashes in bench.

http://108.170.220.120:10117/builders/Test-ChromeOS-Daisy-MaliT604-Arm7-Debug/builds/2608/steps/RunBench/logs/stdio

Original issue's description:
> add readPixels() to SkBitmap
>
> BUG=chromium:390782
>
> Committed: https://skia.googlesource.com/skia/+/c4f216151b6ade70c35fade09a353052f40236b1

R=scroggo@google.com, bsalomon@google.com, reed@google.com
TBR=bsalomon@google.com, reed@google.com, scroggo@google.com
NOTREECHECKS=true
NOTRY=true
BUG=chromium:390782

Author: jcgregorio@google.com

Review URL: https://codereview.chromium.org/382243003