Righteously there shouldn't be any special cases here because
HasTailPolicy and HasMaskPolicy is able to express necessary cases.
This commit is a part of the step-by-step effort to remove
Policy::Scheme::Omit, which completely does not make sense in RVV 1.0
because an RVV instruction always executes with vta and vma set
to a certain value.
This is the 5th commit of a patch-set that aims to change the default policy
for RVV intrinsics from TAMU to TAMA.
Please refer to the cover letter in the 1st commit (D141573) for an
overview.