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