Revert "[RISCV] Store only VNInfo val no in VSETVLIInfo. NFC"

As noted in
https://github.com/llvm/llvm-project/pull/93796#issuecomment-2142752336,
a better way to teach RISCVInsertVSETVLI to work without LiveIntervals
is to set VNInfo to nullptr and teach the various methods to handle it.
We should try that approach first, so we no longer need this pre-commit
patch.

This reverts commit 4b4d3665.