Removed fProgramElements field from IRGenerator

Continuing the process of removing everything from IRGenerator. This
field just mirrors the one in ThreadContext and so is unnecessary.

Change-Id: I3c6672887a03a83ead46788cf2169c7cfccce2cb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/459636
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
4 files changed