Reland "Revert "Omit dead SkSL functions""

This reverts commit fd1173ac719c3c21b363ffdad6b2bb55f7f00113.

Reason for revert: TSAN failure: https://chromium-swarm.appspot.com/task?id=4c93823229fa6a10

Original change's description:
> Revert "Revert "Omit dead SkSL functions""
> 
> This reverts commit 7c969f26bc21b20cb7f4dea497fbdc36d3029709.
> 
> Change-Id: I8fb99f271e2ecaeb83d570cc2d2cf8851bc776f0
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/293338
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

TBR=bsalomon@google.com,brianosman@google.com,ethannicholas@google.com

# Not skipping CQ checks because this is a reland.

Change-Id: Iab3ee5a336074676ebd0b761922ececf189752ef
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/293843
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
9 files changed