Revert "[RISCV] Add policy operand for masked compare and vmsbf/vmsif/vmsof IR"

This reverts commit 10fd2822.

I have a better implementation for those operations without the
additional policy operand.
masked compare and vmsbf/vmsif/vmsof are always tail agnostic so we could
assume undef maskedoff is mask agnostic.

Differential Revision: https://reviews.llvm.org/D122455