remove unused isABitmap code

Waiting on CL to remove calls in Android.

Bug: skia:
Change-Id: I9672ec1602ee3953ab2baa4475f5cdf25e907163
Reviewed-on: https://skia-review.googlesource.com/c/162036
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
7 files changed