Remove texture sampling from GrConfigConversionEffect

BUG=skia:

Change-Id: If5df087d3fe11098f468deab5f2fc8beb782cc83
Reviewed-on: https://skia-review.googlesource.com/10026
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed