[llvm] [NFC][Bitcode] Remove FUNCTION_INST_UNOP abbrevs (PR #146717)

[Nikita Popov via llvm-commits]

nikic wrote:

Yeah, I think we can drop this for now. Without the CodeLen change, the benefit of dropping it is minimal (it will only save emitting two abbrev records, right?)

https://github.com/llvm/llvm-project/pull/146717