[InstSimplify] Remove the remainder loop if we know the mask is always true

We check the loop trip count is known a power of 2 to determine
whether the tail loop can be eliminated in D146199.
However, the remainder loop of mask scalable loop can also be removed
If we know the mask is always going to be true for every vector iteration.
Depend on the assume of power-of-two vscale on D155350

proofs： https://alive2.llvm.org/ce/z/FkTMoy

Fix https://github.com/llvm/llvm-project/issues/63616.

Reviewed By: goldstein.w.n, nikic, david-arm, paulwalker-arm
Differential Revision: https://reviews.llvm.org/D154953