HsCmdArrForm Fixity

We are currently wrapping up https://gitlab.haskell.org/ghc/ghc/-/merge_requests/12842, which moves Fixity declarations into TTG extensions point, and into the haskell syntax, not GHC. But rnCmd for HsCommandArrForm in current master has rnCmd (HsCmdArrForm _ op _ (Just _) [arg1, arg2]) ... It matches on HsCmd GhcPs, which never introduce the `Just` form for fixity. The only place the `Just` form is introduced, is in mkOpFormRn, but this is only ever called from this specific equation. So both can be removed, without changing behaviour. The question is, this code was added for a reason at some point, what has broken in the meantime? Should this be fixed somehow instead of being removed? Alan