[LLVM][NFC] remove unused fields
Here is the commit introducing the fields
It dates back from 2006 and was used by AArch64 backend.
There is no more reference to these fields in the whole codebase so I think it's fine.
Subscribers: javed.absar, kristof.beyls, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D66683