Rename kTexture2DISampler to kITexture2DSampler.

Also remove unused kGrSLTypeCount.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4903

Change-Id: I7f934c56515424b2668886dec2f16296a1256e2c
Reviewed-on: https://skia-review.googlesource.com/4903
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Chris Dalton <csmartdalton@google.com>
6 files changed