Revert of Use dst copies in porter duffer XP to correctly render certain blends. (patchset #4 id:60001 of https://codereview.chromium.org/914003003/)

Reason for revert:
Failing GLProgramTest passing in stupid coeffs

Original issue's description:
> Use dst copies in porter duffer XP to correctly render certain blends.
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/997c6358d94e188b1a7b89a4f86e24cbe0f5a164

TBR=bsalomon@google.com,joshualitt@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/923153003
12 files changed