Remove unused color from all distance field GPs and GrAtlasTextOp

Bug: skia:
Change-Id: I7f2bd68cc4f6ad65660a4415a08777bc71d34ab6
Reviewed-on: https://skia-review.googlesource.com/90522
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
5 files changed