Fix standalone SkSL build after adding SkOnce to SkSLByteCode

Also trim includes in SkSLCompiler while I'm there

Change-Id: I87b27199b84e5e856e0a914f44368313a6f226e4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/242085
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed