Revert of Fixing libpng transform use  (patchset #5 id:80001 of https://codereview.chromium.org/1214203005/)

Reason for revert:
DEPS roll failing

Original issue's description:
> This change:
> - supports kGray correctly
> - avoid extra call to png_get_IHDR by storing the bit depth
> - call transforms as needed
> - checks for tRNS alpha value in RGB and GRAY color types
>
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/9693037fd41b7ce545b44beaa3489dcfd915018c

TBR=scroggo@google.com,msarett@google.com,emmaleer@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1213743004
2 files changed