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/libbsc/abis_om2000_vty.c b/openbsc/src/libbsc/abis_om2000_vty.c
index eb8f4d5..8325e29 100644
--- a/openbsc/src/libbsc/abis_om2000_vty.c
+++ b/openbsc/src/libbsc/abis_om2000_vty.c
@@ -445,7 +445,7 @@
 	install_element(ENABLE_NODE, &om2k_classnum_inst_cmd);
 	install_node(&om2k_node, dummy_config_write);
 
-	bsc_install_default(OM2K_NODE);
+	vty_install_default(OM2K_NODE);
 	install_element(OM2K_NODE, &om2k_reset_cmd);
 	install_element(OM2K_NODE, &om2k_start_cmd);
 	install_element(OM2K_NODE, &om2k_status_cmd);