Make Roster.waitUntilLoaded() package-private

there is no point in having it 'protected', since Roster is not
subclassable.

smack-im/src/main/java/org/jivesoftware/smack/roster/Roster.java

@@ -333,7 +333,7 @@ public final class Roster extends Manager {
         return true;
     }
 
-    protected boolean waitUntilLoaded() throws InterruptedException {
+    boolean waitUntilLoaded() throws InterruptedException {
         final XMPPConnection connection = connection();
         while (!loaded) {
             long waitTime = connection.getPacketReplyTimeout();