Removed fSharedElements field from IRGenerator

Continuing to remove things from IRGenerator. This is another field that
just mirrors state already in ThreadContext.

Change-Id: Ie15842748b55b76ca44c54283b8d9e344f4c670f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/459637
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
4 files changed