title: Knockout: remove all subscriptions from an observable
body: <p>I have an observable that I want to release the memory that is uses.
  When setting in to null, the Garbage Collector is not collecting it becuase other he is referenced in some subscription.</p>
  
  <p>The question is - how can I remove all the subscribers?</p>
  
  <p>for example:</p>
  
  <p>creating:</p>
  
  <pre><code>this.x = ko.observable();
  </code></pre>
  
  <p>removing:</p>
  
  <pre><code>this.x(null);
  </code></pre>
  
  <p>but it is not removed becuase it is referenced in some subscription:</p>
  
  <pre><code>this.y.subscribe(function (newValue) {
     var z = this.x();
  };
  </code></pre>
  
  <p>I dont want to <code>dispose</code> the subscription - becacuse for a new value for <code>x</code> I want <code>y</code> to subscribe to it.</p>
  
  <p>I hope it is clear.</p>
  
  <p>Thanks</p>