remove monkey patch for older versions of tornado

Since we now depend on Tornado >= 3.1, this code path is no longer
necessary

IPython/html/notebookapp.py

@@ -574,30 +574,6 @@ class NotebookApp(BaseIPythonApplication):
             try:
                 self.http_server.listen(port, self.ip)
             except socket.error as e:
-                # XXX: remove the e.errno == -9 block when we require
-                # tornado >= 3.0
-                if e.errno == -9 and tornado.version_info[0] < 3:
-                    # The flags passed to socket.getaddrinfo from
-                    # tornado.netutils.bind_sockets can cause "gaierror:
-                    # [Errno -9] Address family for hostname not supported"
-                    # when the interface is not associated, for example.
-                    # Changing the flags to exclude socket.AI_ADDRCONFIG does
-                    # not cause this error, but the only way to do this is to
-                    # monkeypatch socket to remove the AI_ADDRCONFIG attribute
-                    saved_AI_ADDRCONFIG = socket.AI_ADDRCONFIG
-                    self.log.warn('Monkeypatching socket to fix tornado bug')
-                    del(socket.AI_ADDRCONFIG)
-                    try:
-                        # retry the tornado call without AI_ADDRCONFIG flags
-                        self.http_server.listen(port, self.ip)
-                    except socket.error as e2:
-                        e = e2
-                    else:
-                        self.port = port
-                        success = True
-                        break
-                    # restore the monekypatch
-                    socket.AI_ADDRCONFIG = saved_AI_ADDRCONFIG
                 if e.errno == errno.EADDRINUSE:
                     self.log.info('The port %i is already in use, trying another random port.' % port)
                     continue