Revert of Have DM manually encode its .png outputs. (patchset #2 id:20001 of https://codereview.chromium.org/1304443002/ )

Reason for revert:
derek + Test-Win8-MSVC-ShuttleB-CPU-AVX2-x86_64-Debug

Original issue's description:
> Have DM manually encode its .png outputs.
>
> This eliminates some variability on various axes: different PNG encoders, different libpng versions, different formats (RGB, indexed), different unpremultiplication, different sRGB tags.
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/3cc0dfffb70c0bd08ed8899efcd2e98da86a6ec7

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

Review URL: https://codereview.chromium.org/1297383002
2 files changed