Revert of Make GrGLConfigConversionEffect work for Imagination and some other GPUs. (https://codereview.chromium.org/277323002/)

Reason for revert:
Need to only use the highp variations on GLES contexts not GL contexts.

http://108.170.220.120:10117/builders/Test-Mac10.6-MacMini4.1-GeForce320M-x86_64-Release/builds/3398/steps/RunTests/logs/stdio

Original issue's description:
> Make GrGLConfigConversionEffect work for Imagination and some other GPUs.
>
> BUG=372341
>
> Committed: https://skia.googlesource.com/skia/+/93cf46f7d687128d2ad05762bd65fea6c4539553

R=tomhudson@chromium.org, changjun.yang@intel.com, rmistry@google.com, jcgregorio@google.com
NOTREECHECKS=true
NOTRY=true
BUG=372341

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/377263003
3 files changed