info/Clients: Outdated and misleading, delete

info/Clients: Outdated and misleading, delete

The .NA header promises information on "Clients which communicate well
with the Empire4 Server".  The page doesn't really deliver.  It talks
about client support for asynchronous notifications.  It stopped
listing separate client projects in 4.0.7 (1997).  Not mentioning such
clients isn't just outdated, it's actively misleading.

Perhaps an up-to-date info page on clients would be useful, but I
can't write one right now.  Delete.

Loses a bit of information for client developers that was tacked on in
4.0.7: pointers to dump commands, and an explanation of timestamps.  I
trust client writers can find "info xdump" without this.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>