Remove DSL from GrGaussianConvolutionFragmentProcessor.

Since this is super performance-sensitive, I manually checked to ensure
that the generated code didn't change. Other than differences in
variable name mangling, our final output looks to be identical.

Change-Id: I1bdf012f9b15bafcd85a9e73abfb3fa444459c60
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/540300
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
2 files changed