Revert "@hide ConnectionService APIs."

This reverts commit 86935c406e4a8bb0e2ad871b51009f3603df9e87.

telecomm/java/android/telecom/Connection.java

@@ -19,7 +19,6 @@ package android.telecom;
 import com.android.internal.telecom.IVideoCallback;
 import com.android.internal.telecom.IVideoProvider;
 
-import android.annotation.SystemApi;
 import android.net.Uri;
 import android.os.Handler;
 import android.os.IBinder;
@@ -44,9 +43,7 @@ import java.util.concurrent.ConcurrentHashMap;
  * Implementations are then responsible for updating the state of the {@code Connection}, and
  * must call {@link #destroy()} to signal to the framework that the {@code Connection} is no
  * longer used and associated resources may be recovered.
- * @hide
  */
-@SystemApi
 public abstract class Connection {
 
     public static final int STATE_INITIALIZING = 0;
@@ -876,7 +873,7 @@ public abstract class Connection {
         return mUnmodifiableConferenceableConnections;
     }
 
-    /**
+    /*
      * @hide
      */
     public final void setConnectionService(ConnectionService connectionService) {