remove unused SkFilterProcs

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD
Bug: skia:
Change-Id: I7f9abb3ecb1c7b4fd18a703198c54c6d8f5e1ef7
Reviewed-on: https://skia-review.googlesource.com/20429
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
5 files changed