Yeet unnecessary param envs We don't need to pass in param-envs around in the lexical region resolution code (or in `MatchAgainstFreshVars` in the solver), since it is only used to eval some consts in `structurally_relate_tys` which I removed. This is in preparation for normalizing the outlives clauses in `ParamEnv` for the new trait solver. r? lcnr