remove unused SkLightingShader

Change-Id: I60a3569b47b599b710c0f3a9522241748f15360d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/280409
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
20 files changed