Incorrect comment for expand_single_inheritance_child

Here is part of comments for expand_single_inheritance_child:

* expand_single_inheritance_child
* Expand a single inheritance child, if needed.
*
* If this is a temp table of another backend, we'll return without doing
* anything at all. Otherwise, build a RangeTblEntry and an
AppendRelInfo, if
* appropriate, plus maybe a PlanRowMark.

The sentence "If this is a temp table of another backend, we'll return
without doing anything at all" is not correct, because that function
doesn't even check whether the given child is such a temp table. (The
caller does, so that function assumes that the given child is not such a
temp table.) So I think we should remove that sentence entirely. Also,
I think we should remove "if needed" from the headline: Expand a single
inheritance child, if needed. IMO I don't think that "Expand a single
inheritance child" says much, so I'd like to propose changing that part
simply to something like this:

* expand_single_inheritance_child
* Build a RangeTblEntry and an AppendRelInfo, if appropriate, plus
* maybe a PlanRowMark.

Attached is a patch for that.

Best regards,
Etsuro Fujita