Revert "[db] Keep track of the current gsm_network"

This was a stupid decision. We will have to assign the
network at some other place. The problem will be a problem
when we have two gsm_networks in one process and the same
subscriber is traveling in both networks.
diff --git a/tests/db/db_test.c b/tests/db/db_test.c
index bbca585..6962aa3 100644
--- a/tests/db/db_test.c
+++ b/tests/db/db_test.c
@@ -50,7 +50,7 @@
 
 int main() {
 
-	if (db_init("hlr.sqlite3", NULL)) {
+	if (db_init("hlr.sqlite3")) {
 		printf("DB: Failed to init database. Please check the option settings.\n");
 		return 1;
 	}