The bogus calls in remove_self_join_rel()

I noticed these two calls in remove_self_join_rel():

adjust_relid_set(root->all_result_relids, toRemove->relid, toKeep->relid);
adjust_relid_set(root->leaf_result_relids, toRemove->relid, toKeep->relid);

There's no comment explaining them, and as far as I can tell they do
nothing: adjust_relid_set returns a Relids and does not modify the
input in place.

Rather than make the calls do the cleanup they pretend to do, I think
a better way is to replace them with assertions: toRemove->relid is
not a member of either set. This is true as these two sets contain
only parse->resultRelation (rejected as an SJE candidate to preserve
EvalPlanQual) and inheritance children of the target, which never
appear in the joinlist that SJE scans for candidates.

Thoughts?

- Richard