Drop unused shader support for sample variables

Bug: skia:
Change-Id: I9e2b7da8c916703027d8dd4303ae67f4e69bcf87
Reviewed-on: https://skia-review.googlesource.com/107356
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
32 files changed