No need to `validate_alias_bound_self_from_param_env` in `assemble_alias_bound_candidates`
We already fully normalize the self type before we reach `assemble_alias_bound_candidates`, so there's no reason to double check that a projection is truly rigid by checking param-env bounds.
I think this is also blocked on us making sure to always normalize opaques: #120549.
r? lcnr
