Revert "[DWARF] Create subprogram's DIE in DISubprogram's unit"
This reverts commit ef0dcb506300dc9644e8000c6028d14214be9d97.
This change is causing a lot of compiler crashes inside, sorry I don't have a
small repro/stacktrace with symbols to share right now.
Differential Revision: https://reviews.llvm.org/D95622
