remove AVX raster pipeline stages

It's rare these days to find a CPU with AVX but not AVX2.

The memsets still make sense to leave, as we don't do anything
different there even with AVX2... all the instructions we want
are available with AVX.

Change-Id: I412f95c4548cfcc56c19b72348deceee83ba0610
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/294319
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed