Revert of Add tokens and entry points for KHR_blend_equation_advanced

Revert of Add tokens and entry points for KHR_blend_equation_advanced (patchset #3 id:40001 of https://codereview.chromium.org/1039693004/)

Reason for revert:
We're getting repeated crashes since this CL landed when we try to evaluate a roll into Chrome on our bots. (https://uberchromegw.corp.google.com/i/client.skia/builders/Linux%20Tests/builds/1902)

Our initial reflex is to put a #if 0 around this code (just like the immediately following lines 334-338 in GrGLInterface.cpp), but the error isn't what the GPU team expected to see if that was all we needed, so we're reverting now and asking you to resubmit tomorrow after running more thorough tests.

Original issue's description:
> Add tokens and entry points for KHR_blend_equation_advanced
> 
> BUG=skia:
> 
> Committed: https://skia.googlesource.com/skia/+/8e578859f80b46a63144add215955221017d3609

TBR=markkilgard@gmail.com,bsalomon@google.com,cdalton@nvidia.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Committed: https://skia.googlesource.com/skia/+/2575f317d3fa977676279097332955c20ad46044

[tomhudson, 2015-04-21 21:16:29]

Created Revert of Add tokens and entry points for KHR_blend_equation_advanced

[commit-bot: I haz the power, 2015-04-21 21:16:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1101593002/1

[commit-bot: I haz the power, 2015-04-21 21:16:57]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/2575f317d3fa977676279097332955c20ad46044