[dev.simd] cmd/compile, simd: adjust Shift.* operations

[dev.simd] cmd/compile, simd: adjust Shift.* operations

This CL does:
1. Removes ShiftRightSignExtended, default signed vectors to shift
   arithmetic, and unsigned to shift logical.
2. Add the missing Shifts which were left out by YAML error in the
   generator.

This CL is generated by CL 687595.

Change-Id: I663115498adb91c82e89a8476e6748794e997cfa
Reviewed-on: https://go-review.googlesource.com/c/go/+/687596
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>