remove unused readBitmapAsImage from readbuffer

Bug: skia:
Change-Id: Ic200ec39999a06f407de29e15b646baddb9e341d
Reviewed-on: https://skia-review.googlesource.com/76982
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
5 files changed