Remove unused functions and members from PipelineStageCodeGenerator

Change-Id: Ib5318575ab929f1e911c8cb13753fd6d19d48818
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/266202
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed