Remove PLS support from SkSL

Change-Id: I885149c73be63c223ac88a697ffe046a7f8384d0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/372116
Reviewed-by: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
12 files changed