Rip out Socket.IO implementation

No two ways about it: if we're going to be "just a WSGI library" then we
can't implement Socket.IO ourselves. Instead we'll have to figure out
how to use gevent-socketio or similar. That rebuilding step is on the
other side of the Great Purge of 2014.
Watch the world burn.

This rips out network_address and network_engine and the rest of
sockets.W