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/include/openbsc/db.h b/include/openbsc/db.h
index 2036832..61a3ac4 100644
--- a/include/openbsc/db.h
+++ b/include/openbsc/db.h
@@ -26,7 +26,7 @@
 #include <openbsc/gsm_subscriber.h>
 
 /* one time initialisation */
-int db_init(const char *name, struct gsm_network *network);
+int db_init(const char *name);
 int db_prepare();
 int db_fini();