Remove extra word from comment.
David Rowley, who also was the primary author of the patch that
added this function; the attribution in my previous commit,
84940644de931f331433b35e3a391822671f8c9c, was incorrect due to
sloppiness on my part.
Discussion: http://postgr.es/m/CAKJS1f_0iSiLQsf_c06AzOWAc3eS6ePjjVQFpcFv3W-O5aktnQ@mail.gmail.com