[AArch64] Clean up assorted usage of hasOneUse/use_instructions [9/14]

Summary:
Use the variants of these APIs which skip over debug instructions. This
is mostly a cleanup, but it does fix a debug-variance issue which causes
addsub-shifted.ll and addsub_ext.ll to fail when debug info is inserted
by -mir-debugify.

Reviewers: aemerson, paquette

Subscribers: kristof.beyls, hiraditya, jfb, danielkiss, llvm-commits, aprantl

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78262