Revert of Fixing libpng transform use

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:

Committed: https://skia.googlesource.com/skia/+/6c90e09575c1a77aee060aa475fdb3d25a17d6a0

[jvanverth1, 2015-07-02 17:35:14]

Created Revert of Fixing libpng transform use

[commit-bot: I haz the power, 2015-07-02 17:35:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1213743004/1

[commit-bot: I haz the power, 2015-07-02 17:35:27]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/6c90e09575c1a77aee060aa475fdb3d25a17d6a0

[scroggo, 2015-07-07 13:08:53]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1215853005/ by scroggo@google.com.

The reason for reverting is: This appears to have been reverted in order to fix
the DEPS roll in https://codereview.chromium.org/1214943004/

However, it only affects SkCodec, which is not used by Chromium. Relanding.