Delete unused onSignOut method

Once upon a time Gerrit performed a sign-out by just deleting the
cookie and updating the DOM to remove signed-in content. This is
not true anymore, the entire page is refreshed to delete any data
that is private to a signed-in account, and to ensure the server
can clear the correct HttpOnly cookies to actually do a sign-out.

Since that behavior change, this onSignOut method is dead code.

Change-Id: I7d7922f3a38fdcd03615866d0d693088660e1a31

gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeScreen.java

@@ -117,14 +117,6 @@ public class ChangeScreen extends Screen
     this(c.getId());
   }
 
-  @Override
-  public void onSignOut() {
-    super.onSignOut();
-    if (starChange != null) {
-      starChange.setVisible(false);
-    }
-  }
-
   @Override
   protected void onLoad() {
     super.onLoad();