[ARM][MVE] Remove old tail predicates

Remove any predicate that we replace with a vctp intrinsic, and try
to remove their operands too. Also look into the exit block to see if
there's any duplicates of the predicates that we've replaced and
clone the vctp to be used there instead.

Differential Revision: https://reviews.llvm.org/D67709

llvm-svn: 372567