PingManager: Don't register IQProvider since this is done by smack.providers already. This line was actually a leftover from aSmack development.

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@13406 b35dd754-fafc-0310-a699-88a17e54d16e
fix typo in PingManager.getInstanceFor() function name