Eliminate dead local variables from dehydrated code.

This should address the root cause of http://review.skia.org/538045.

We currently don't eliminate unreferenced names from the symbol table,
although that'd be free money if we wanted to do it.

Change-Id: I712e23e6a4f3cb48c2b5ae68f042e13031d5f632
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/540038
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed