Revert "[RISCV][ISel] Combine scalable vector add/sub/mul with zero/sign extension (#72340)"

This reverts most of commit 5b155ae.
I have left the new test file, but regenerated the checks.

This causes failures in our downstream testing. The input types
to the extends need to be checked so we don't create RISCVISD::VZEXT_VL
with illegal or unsupported input type.

Author: topperc