Revert "Revert "clean up sksl dead variable handling""

This reverts commit e0a33e28e2786fb17be2edf28e04cd62bfe4ec1e.

Bug: skia:
Change-Id: Iab31ec1ee091aacc3ba854ad91e71840c911f52e
Reviewed-on: https://skia-review.googlesource.com/20506
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
4 files changed