Removed useless reference to RxJS typing

Since the typing is now part of RxJS, referencing it (which is causing a
nuget package dependency) will cause a problem by having twice the save
references in the samme app.

knockout.rx/knockout.rx.d.ts

@@ -4,7 +4,6 @@
 // Definitions: https://github.com/borisyankov/DefinitelyTyped
 
 /// <reference path="../knockout/knockout.d.ts"/>
-/// <reference path="../rx.js/rx.d.ts"/>
 
 interface KnockoutSubscribableFunctions<T> {
 	toObservable(event?: string): Rx.Observable<T>;
@@ -21,6 +20,8 @@ interface KnockoutComputedFunctions<T> {
 }
 
 declare module Rx {
+	interface ISubject<T> { }
+
 	interface Observable<T> {
 		toKoSubscribable(): KnockoutSubscribable<T>;
 		toKoObservable(initialValue?: T): KnockoutObservable<T>;