dissolve libcommon: move talloc ctx into msc_main.c, drop talloc_ctx.c

Drop tall_bsc_ctx; in mncc_sock_init(), talloc the mncc_sock_state from
gsm_network.

In tests or utils, move from using an extern tall_bsc_ctx to a local root
context pointer.

Change-Id: I92c252be1d1e7634f1653de47d37c99d77d9501c
diff --git a/src/libcommon/gsup_test_client.c b/src/libcommon/gsup_test_client.c
index 3e88689..add98e4 100644
--- a/src/libcommon/gsup_test_client.c
+++ b/src/libcommon/gsup_test_client.c
@@ -275,8 +275,6 @@
 	}
 }
 
-void *tall_bsc_ctx = NULL;
-
 /* default categories */
 static struct log_info_cat default_categories[] = {
 };
@@ -294,7 +292,7 @@
 
 	osmo_init_logging(&gsup_test_client_log_info);
 
-	g_gc = gsup_client_create("GSUPTEST", server_host, server_port,
+	g_gc = gsup_client_create(NULL, "GSUPTEST", server_host, server_port,
 				  gsupc_read_cb, NULL);