remove imageinfo flatten altogether

If SkImageInfo flatten and unflatten aren't referenced outside
of one test, perhaps they can be removed altogether.

R=reed@google.com

Bug: skia:6898
Change-Id: Ia6f82b66d4496a628ad95c386d1865793f3e31a9
Reviewed-on: https://skia-review.googlesource.com/115074
Commit-Queue: Cary Clark <caryclark@skia.org>
Reviewed-by: Mike Reed <reed@google.com>
3 files changed