Small tidyup for commit d41a178b, part II.

Small tidyup for commit d41a178b, part II.

Further to commit 6a9229da, checking for NULL is now redundant.  An "out
of memory" error would have been thrown already by palloc() and treated
as FATAL, so we can delete a few more lines.

Back-patch to all releases, like those other commits.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: http://postgr.es/m/4040668.1679013388%40sss.pgh.pa.us