unix_msg: remove cookie from unix_msg_init

unix_msg: remove cookie from unix_msg_init

"pid" and "sock" are sufficient I guess as randomizers to distinguish messages.
In theory, a pid could be recycled very quickly, which might mix up in-flight
messages. But once a few messages have passed, "cookie" would be incremented as
another indicator of a fresh message.

Why? Remove messages_dgm dependency on samba-util

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>