[mgcp] Remove unused method from the mgcp

This was removed when sending the RSIP was
removed from the code.
diff --git a/openbsc/src/mgcp/mgcp_protocol.c b/openbsc/src/mgcp/mgcp_protocol.c
index 5ae3570..7ad4e0a 100644
--- a/openbsc/src/mgcp/mgcp_protocol.c
+++ b/openbsc/src/mgcp/mgcp_protocol.c
@@ -119,12 +119,6 @@
 	return cfg->last_call_id;
 }
 
-/* FIXIME/TODO: need to have a list of pending transactions and check that */
-static unsigned int generate_transaction_id()
-{
-	return abs(rand());
-}
-
 /*
  * array of function pointers for handling various
  * messages. In the future this might be binary sorted