The destination parameter is removed for non-policy unmasked vslidedown
intrinsics.
The default policy for non-policy (implicit) vslidedown intrinsics will
be tail agnostic and mask undisturbed.
This is the 3rd commit of a patch-set that aims to remove the
IsPrototypeDefaultTU special case for the rvv-intrinsics.
Please refer to the cover letter in the 1st commit (D140895) for an
overview.