Add more comments in the code and remove unused code file

lib/realtime.js

@@ -518,13 +518,16 @@ function disconnect(socket) {
 	var noteId = socket.noteId;
     var note = notes[noteId];
     if (note) {
+        // delete user in users
         delete note.users[socket.id];
+        // remove sockets in the note socks
         do {
             var index = note.socks.indexOf(socket);
             if (index != -1) {
                 note.socks.splice(index, 1);
             }
         } while (index != -1);
+        // remove note in notes if no user inside
         if (Object.keys(note.users).length <= 0) {
             if (note.server.isDirty) {
                 updateNote(note, function (err, _note) {