Cleanup writeComponentwiseMatrixBinary implementation.

The previous version took integer SpvOps, but GLSL and SkSL have no
support for integer matrices, so this was unnecessary. Also, hand-rolled
SpvOpCompositeConstruct generation has been replaced with an equivalent
call to `writeComposite`.

Change-Id: I4992bab80cc563acef49b5047b5ab39fd5840c1e
Bug: skia:11985
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/408636
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
2 files changed