[NFC][TargetParser] Remove llvm/Support/AArch64TargetParser.h

Removes the forwarding header `llvm/Support/AArch64TargetParser.h`.

I am proposing to do this for all the forwarding headers left after
rGf09cf34d - for each header:
- Update all relevant in-tree includes
- Remove the forwarding Header

Differential Revision: https://reviews.llvm.org/D140999