Simplify VertexRegenerator GrStrikeCache handling

The SubRun has access to the GrStrikeCache pointer, there is
no need to pass it around the VertexRegenerator.

Change-Id: I867b1b29b29e595f92ad57505dcd27dd0f6b726f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264649
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
4 files changed