[RISCV] Remove unnecessary patterns for tail agnostic FP intrinsics with rounding mode. (#94498)

These are patterns that explicitly check for undef. Similar patterns do
not exist without rounding mode. The vsetvli insertion pass should be
able to detect that the passthru is undef.

The test changes seem to be a deficiency in identifying passthru being
undef in the vsetvli inserter for -O0.