[DWARFVerifier] Use the new location list api

Summary:
Instead of going to the debug_loc section directly, use new
DWARFDie::getLocations instead. This means that the code will now
automatically support debug_loclists sections.

This is the last usage of the old debug_loc methods, and they can now be
removed.

Reviewers: dblaikie, JDevlieghere, aprantl, SouraVX

Subscribers: hiraditya, probinson, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70534