Hide multi-endpoint APIs.

Per feature council decision, the multi-endpoint APIs will be @hide for
the N release.

Bug: 28196918
Change-Id: Ia80b089bc754ce87ca208382eb79442b5265844d

telecomm/java/android/telecom/InCallService.java

@@ -457,6 +457,7 @@ public abstract class InCallService extends Service {
      * @param call The call the event is associated with.
      * @param event The event.
      * @param extras Any associated extras.
+     * @hide
      */
     public void onConnectionEvent(Call call, String event, Bundle extras) {
     }