[VTY] Remove OpenBSC specific node-exit handling from src/vty

The idea is to move the VTY code into libosmocore at some point,
and for that we need to eliminate OpenBSC specifics from it
diff --git a/openbsc/src/vty_interface.c b/openbsc/src/vty_interface.c
index 8af9153..0ceab5b 100644
--- a/openbsc/src/vty_interface.c
+++ b/openbsc/src/vty_interface.c
@@ -1954,6 +1954,7 @@
 	install_element(CONFIG_NODE, &cfg_net_cmd);
 	install_node(&net_node, config_write_net);
 	install_default(GSMNET_NODE);
+	install_element(GSMNET_NODE, &ournode_exit_cmd);
 	install_element(GSMNET_NODE, &cfg_net_ncc_cmd);
 	install_element(GSMNET_NODE, &cfg_net_mnc_cmd);
 	install_element(GSMNET_NODE, &cfg_net_name_short_cmd);
@@ -1986,6 +1987,7 @@
 	install_element(GSMNET_NODE, &cfg_bts_cmd);
 	install_node(&bts_node, config_write_bts);
 	install_default(BTS_NODE);
+	install_element(BTS_NODE, &ournode_exit_cmd);
 	install_element(BTS_NODE, &cfg_bts_type_cmd);
 	install_element(BTS_NODE, &cfg_description_cmd);
 	install_element(BTS_NODE, &cfg_no_description_cmd);
@@ -2023,6 +2025,7 @@
 	install_element(BTS_NODE, &cfg_trx_cmd);
 	install_node(&trx_node, dummy_config_write);
 	install_default(TRX_NODE);
+	install_element(TRX_NODE, &ournode_exit_cmd);
 	install_element(TRX_NODE, &cfg_trx_arfcn_cmd);
 	install_element(TRX_NODE, &cfg_description_cmd);
 	install_element(TRX_NODE, &cfg_no_description_cmd);
@@ -2035,6 +2038,7 @@
 	install_element(TRX_NODE, &cfg_ts_cmd);
 	install_node(&ts_node, dummy_config_write);
 	install_default(TS_NODE);
+	install_element(TS_NODE, &ournode_exit_cmd);
 	install_element(TS_NODE, &cfg_ts_pchan_cmd);
 	install_element(TS_NODE, &cfg_ts_e1_subslot_cmd);