Fix deprecation warning that comes from GWT

One should use
    main = new DisclosurePanel(text);
    main.setOpen(isOpen);
instead of
    main = new DisclosurePanel(text, isOpen);

Change-Id: I49e2a2c81c851519ff5cd9c347ba8ad8c9e8a498

gerrit-gwtui/src/main/java/com/google/gerrit/client/ui/ComplexDisclosurePanel.java

@@ -38,7 +38,8 @@ public class ComplexDisclosurePanel extends Composite implements
     // other modification of its header. We're stuck with injecting
     // into the DOM directly.
     //
-    main = new DisclosurePanel(text, isOpen);
+    main = new DisclosurePanel(text);
+    main.setOpen(isOpen);
     final Element headerParent;
     {
       final Element table = main.getElement();