nimble/gap: Remove notification for update process timeout.

The connection parameter update process has a hard-coded 40-second timeout,
but in reality, the time it takes to complete a connection parameter might take longer, as it
depends on the connection interval and when controller deciders to do it.
This patch changes meaning of this 40 sec timer to be only a guard so the application
does not perform too many connection update parameter requests.
Now when timeout fires, application will not be notified about that and link will not be dropped.

nimble/host/src/ble_gap.c

@@ -1943,7 +1943,6 @@ ble_gap_update_timer(void)
         ble_hs_unlock();
 
         if (entry != NULL) {
-            ble_gap_update_notify(conn_handle, BLE_HS_ETIMEOUT);
             ble_gap_update_entry_free(entry);
         }
     } while (entry != NULL);

nimble/host/test/src/ble_gap_test.c

@@ -2982,9 +2982,6 @@ TEST_CASE_SELF(ble_gap_test_case_update_timeout)
         .max_ce_len = 456,
     };
 
-    /* No L2CAP. */
-    ble_gap_test_util_update_no_l2cap_tmo(&params, 1);
-
     /* L2CAP - Local unsupported; L2CAP timeout. */
     ble_gap_test_util_update_l2cap_tmo(&params, BLE_ERR_UNKNOWN_HCI_CMD, 0, 0);