Make Connection.Listener methods package private.

To prevent using these outside of the API surface, making package private
so we don't get tempted to use in the framework.

Bug: 141576016
Test: Manual smoke test.
Test: Run unit tests.
Test: Run CTS tests.
Change-Id: Ife3a82371b018b74efbe10e11015526d7aaeb7a9

telecomm/java/android/telecom/Connection.java

@@ -857,7 +857,7 @@ public abstract class Connection extends Conferenceable {
     }
 
     /** @hide */
-    public abstract static class Listener {
+    abstract static class Listener {
         public void onStateChanged(Connection c, int state) {}
         public void onAddressChanged(Connection c, Uri newAddress, int presentation) {}
         public void onCallerDisplayNameChanged(
@@ -2005,7 +2005,7 @@ public abstract class Connection extends Conferenceable {
      *
      * @hide
      */
-    public final Connection addConnectionListener(Listener l) {
+    final Connection addConnectionListener(Listener l) {
         mListeners.add(l);
         return this;
     }
@@ -2018,7 +2018,7 @@ public abstract class Connection extends Conferenceable {
      *
      * @hide
      */
-    public final Connection removeConnectionListener(Listener l) {
+    final Connection removeConnectionListener(Listener l) {
         if (l != null) {
             mListeners.remove(l);
         }