Fix aclitemout() to work during early bootstrap.

Fix aclitemout() to work during early bootstrap.

"initdb -d" has been broken since commit f95d73ed4, because I changed
aclitemin to work in bootstrap mode but failed to consider aclitemout.
That routine isn't reached by default, but it is if the elog message
level is high enough, so it needs to work without catalog access too.

This patch just makes it use its existing code paths to print role
OIDs numerically.  We could alternatively invent an inverse of
boot_get_role_oid() and print them symbolically, but that would take
more code and it's not apparent that it'd be any better for debugging
purposes.

Reported-by: Greg Burd <greg@burd.me>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/4416.1773328045@sss.pgh.pa.us