Fix psql describe commands' handling of ACL columns for old servers.
Commit
d1379ebf4 carelessly broke printACLColumn for pre-9.4 servers,
by using the cardinality() function which we introduced in 9.4.
We expect psql's describe-related commands to work back to 9.2, so
this is bad. Use the longstanding array_length() function instead.
Per report from Christoph Berg. Back-patch to v17.
Discussion: https://postgr.es/m/ZvLXYglRS6hMMhtr@msg.df7cb.de