Make 'uniform' modifier on SkSL samplers/textures optional.

The `uniform` modifier on sampler declarations is a holdover
from the original GLSL syntax and doesn't really make sense in
a modern context. It is no longer necessary in SkSL; the GLSL
code generator synthesizes it as needed.

Bug: b/295169976
Change-Id: Ibe1ff0abf5ab244d5b1f0bbbdc306ba9989f00f2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/746097
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Arman Uguray <armansito@google.com>
Commit-Queue: Arman Uguray <armansito@google.com>
58 files changed