remove i16x2 ops

These are neat but mostly just a distraction for now.
I've left all the assembly in place and unit tested
to make putting these back easy when we want to.

Change-Id: Id2bd05eca363baf9c4e31125ee79e722ded54cb7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/283307
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
8 files changed