removing datlastsysoid

Hi,

While reviewing another patch, I noticed that it slightly adjusted the
treatment of datlastsysoid. That made me wonder what datlastsysoid is
used for, so I started poking around and discovered that the answer,
at least insofar as I can determine, is "nothing". The documentation
claims that the value is useful "particularly to pg_dump," which turns
out not to be true any more. Tom's recent commit,
30e7c175b81d53c0f60f6ad12d1913a6d7d77008, to remove pg_dump/pg_dumpall
support for dumping from pre-9.2 servers, removed all remaining uses
of this value from the source tree. It's still maintained. We just
don't do anything with it.

Since that doesn't seem like an especially good idea, PFA a patch to
remove it. Note that, even prior to that commit, it wasn't being used
for anything when dumping modern servers, so it would still have been
OK to remove it from the current system catalog structure. Now,
though, we can remove all references to it.

--
Robert Haas
EDB: http://www.enterprisedb.com