Revert "@hide ConnectionService APIs."

This reverts commit 86935c406e4a8bb0e2ad871b51009f3603df9e87.

telecomm/java/android/telecom/RemoteConference.java

@@ -18,7 +18,6 @@ package android.telecom;
 
 import com.android.internal.telecom.IConnectionService;
 
-import android.annotation.SystemApi;
 import android.os.RemoteException;
 
 import java.util.Collections;
@@ -29,9 +28,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
 
 /**
  * Represents a conference call which can contain any number of {@link Connection} objects.
- * @hide
  */
-@SystemApi
 public final class RemoteConference {
 
     public abstract static class Callback {