vty: Use vty_install_default() instead of bsc_install_default()

Remove ournode_exit_cmd, ournode_end_cmd, and bsc_install_default()
since this functionality is provided by the current libosmocore.

Replace calls to bsc_install_default() by call to
vty_install_default() with the following semantic patch:

    @rule1@
    expression N;
    @@
    - bsc_install_default(N);
    + vty_install_default(N);

Ticket: OW#952
Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_vty.c b/openbsc/src/osmo-bsc_nat/bsc_nat_vty.c
index 72a6801..8dea34e 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_vty.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_vty.c
@@ -1192,7 +1192,7 @@
 	/* nat group */
 	install_element(CONFIG_NODE, &cfg_nat_cmd);
 	install_node(&nat_node, config_write_nat);
-	bsc_install_default(NAT_NODE);
+	vty_install_default(NAT_NODE);
 	install_element(NAT_NODE, &cfg_nat_msc_ip_cmd);
 	install_element(NAT_NODE, &cfg_nat_msc_port_cmd);
 	install_element(NAT_NODE, &cfg_nat_auth_time_cmd);
@@ -1233,14 +1233,14 @@
 	install_element(NAT_NODE, &cfg_nat_pgroup_cmd);
 	install_element(NAT_NODE, &cfg_nat_no_pgroup_cmd);
 	install_node(&pgroup_node, config_write_pgroup);
-	bsc_install_default(PGROUP_NODE);
+	vty_install_default(PGROUP_NODE);
 	install_element(PGROUP_NODE, &cfg_pgroup_lac_cmd);
 	install_element(PGROUP_NODE, &cfg_pgroup_no_lac_cmd);
 
 	/* BSC subgroups */
 	install_element(NAT_NODE, &cfg_bsc_cmd);
 	install_node(&bsc_node, config_write_bsc);
-	bsc_install_default(NAT_BSC_NODE);
+	vty_install_default(NAT_BSC_NODE);
 	install_element(NAT_BSC_NODE, &cfg_bsc_token_cmd);
 	install_element(NAT_BSC_NODE, &cfg_bsc_lac_cmd);
 	install_element(NAT_BSC_NODE, &cfg_bsc_no_lac_cmd);