CVE-2015-5370: s4:rpc_server: remove pointless dcesrv_find_context() from dcesrv_bind()

BIND is the first pdu, which means the list of contexts is always empty.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11344

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Günther Deschner <gd@samba.org>
