fix merge issue in python binding

git-svn-id: svn://svn.code.sf.net/p/libtorrent/code@10509 a83610d8-ad2a-0410-a6ab-fc0612d85776
collapse dht::refresh into dht::bootstrap, since it is now a redundant class

git-svn-id: svn://svn.code.sf.net/p/libtorrent/code@10510 a83610d8-ad2a-0410-a6ab-fc0612d85776