Do not check for register_enb_pending

The test seemingly ensures that this code block is hit only once.
However, if we enable later activation of MMEs, it will be hit a second
(and third, ...) time. The only thing in guards against, though, is an
INIT message to the L1L2 thread, when register_enb_pending == 0, which
should only be sent once.  Therefore, functionality won't be changed if
register_enb_pending becomes negative, and the assert can be removed.

openair2/ENB_APP/enb_app.c

@@ -273,7 +273,6 @@ void *eNB_app_task(void *args_p) {
         if (EPC_MODE_ENABLED) {
           LOG_I(ENB_APP, "[eNB %d] Received %s: associated MME %d\n", instance, ITTI_MSG_NAME (msg_p),
                 S1AP_REGISTER_ENB_CNF(msg_p).nb_mme);
-          DevAssert(register_enb_pending > 0);
           register_enb_pending--;
 
           /* Check if at least eNB is registered with one MME */