[llvm] [Mips][NFC] Garbage collect unused code (PR #85499)

[YunQiang Su via llvm-commits]

wzssyqa wrote:

Go ahead please.
I left these lines as I thought that they will be useful if we'd like to support `-mabicalls -mno-shared` in future.

https://github.com/llvm/llvm-project/pull/85499