mgcp_protocol: get rid of policy_cb and change_cb

The two callback functions policy_cb and change_cb are essentially dead
code. They also make the code more difficult to read and understand.
Lets remove them.

Change-Id: I19f67db1c56473f47338b56114f6bbae8981d067
diff --git a/include/osmocom/mgcp/mgcp_protocol.h b/include/osmocom/mgcp/mgcp_protocol.h
index 7ab283d..df134ab 100644
--- a/include/osmocom/mgcp/mgcp_protocol.h
+++ b/include/osmocom/mgcp/mgcp_protocol.h
@@ -16,6 +16,8 @@
 	int pkt_period_max; /* time in ms */
 };
 
+char *mgcp_debug_get_last_endpoint_name(void);
+
 char *get_lco_identifier(const char *options);
 int check_local_cx_options(void *ctx, const char *options);