Currently, there are no built-in functions that are SECURITY DEFINER.
But we just found an instance where one was mistakenly marked that way,
so it seems prudent to add a test about it.  If we ever grow some
functions that are intentionally SECURITY DEFINER, we can alter the
expected output of this test, or adjust the query to filter out functions
for which it's okay.

Per suggestion from Robert Haas.

Discussion: https://postgr.es/m/CA+TgmoYXg7McY33+jbWmG=rS-HNUur0S6W8Q8kVNFf7epFimVA@mail.gmail.com