Revert "clean up sksl dead variable handling"

This reverts commit b29dd819c9f4cc0f33c24a10b128c363a4c83a6f.

Reason for revert: asan errors

Original change's description:
> clean up sksl dead variable handling
> 
> Change-Id: I301e82bf87d976e59a02b0f383da67eaf5a8795a
> Reviewed-on: https://skia-review.googlesource.com/18494
> Reviewed-by: Chris Dalton <csmartdalton@google.com>
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

TBR=csmartdalton@google.com,ethannicholas@google.com

Change-Id: I32b3c6a04a014b31360d92b3f85491b01e8a381c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/20480
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
4 files changed