nbd: remove incorrect coroutine_fn annotations

nbd_co_establish_connection_cancel() cancels a coroutine but is not called
from coroutine context itself, for example in nbd_cancel_in_flight()
and in timer callbacks reconnect_delay_timer_cb() and open_timer_cb().

Reviewed-by: Alberto Faria <afaria@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220922084924.201610-5-pbonzini@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

include/block/nbd.h

@@ -424,6 +424,6 @@ QIOChannel *coroutine_fn
 nbd_co_establish_connection(NBDClientConnection *conn, NBDExportInfo *info,
                             bool blocking, Error **errp);
 
-void coroutine_fn nbd_co_establish_connection_cancel(NBDClientConnection *conn);
+void nbd_co_establish_connection_cancel(NBDClientConnection *conn);
 
 #endif