libcli/auth: if we require aes we don't need to require arcfour nor strong key

libcli/auth: if we require aes we don't need to require arcfour nor strong key

But we can send arcfour and strong key on the wire and don't need to
remove them from the proposed flags.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15425

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>