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

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

Looks like we're moving ahead with CodeLen increasing to 5 bits.

@nikic should we abandon this? It looks like it does slightly improve sizes overall, but could have a negative affect on some workloads... seems safer to drop it now that we don't need to keep CodeLen down. I'm happy either way.

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