Remove sarcastic comments

... apparently I wrote them, and I don't understand them. There is *supposed*
to be a global flux dispatcher.

This reverts commit c0de0870ed.

src/dispatcher.js

@@ -41,9 +41,6 @@ class MatrixDispatcher extends flux.Dispatcher {
     }
 }
 
-// XXX this is a big anti-pattern, and makes testing hard. Because dispatches
-// happen asynchronously, it is possible for actions dispatched in one thread
-// to arrive in another, with *hilarious* consequences.
 if (global.mxDispatcher === undefined) {
     global.mxDispatcher = new MatrixDispatcher();
 }