Remove  GLSL memory qualifiers from SkSL

These were all unused, and only implemented on one backend.

Change-Id: Ibd2fcef1a971e6c1bd9da0784c5d852a60708484
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/372117
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
15 files changed