[X86][SSE] Remove SSE ADDUS/SUBUS saturation intrinsics from schedule/stack tests

These are already being autoupgraded, currently to an IR sequence, but best to replace them with generic llvm uadd_sat/usub_sat intrinsics (which D55855 will be doing shortly anyhow).

The avx512 masked cases need doing as well but require a bit of tidyup first.

llvm-svn: 349615