fix(e2e): remove invalid syntax usage (#2687)

Author: filipesilva

public/docs/_examples/template-syntax/ts/app/app.component.html

@@ -242,9 +242,6 @@ <h3>
 
   <button [attr.disabled]="!isUnchanged">Disabled as well</button>
 
-  <!-- can't remove it with [attr.disabled] either -->
-  <button disabled [attr.disabled]>Still disabled</button>
-
   <!-- we'd have to remove it with property binding -->
   <button disabled [disabled]="false">Enabled (but inert)</button>
 </div>