This eliminates a handful of useless statements. They were harmless, but
presumably this saves optimization work for the GLSL compiler.
(Patterned after http://review.skia.org/496377 )
Change-Id: Ibe135750488a9917b982dcac67f22b3765412ee1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/496599
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
