Tighten up creation of the GrProgramDesc and remove some unnecessary checks

This takes care of some of the deferred work from:

https://skia-review.googlesource.com/c/skia/+/244118 (Add GrProgramInfo to centralize management of program information)

Bug: skia:9455
Change-Id: If1cdfc0a0614babd18f7f4bccd445e03a6dbb9ae
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/247301
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
8 files changed