remove dispose code in keyboard help, phetsims/scenery-phet#810

Signed-off-by: Michael Kauzmann <[email protected]>

js/HomeScreenKeyboardHelpContent.ts

@@ -10,22 +10,11 @@ import { Node } from '../../scenery/js/imports.js';
 import joist from './joist.js';
 
 class HomeScreenKeyboardHelpContent extends Node {
-  private readonly disposeHomeScreenKeyboardHelpContent: () => void;
-
   public constructor() {
     const basicActionsKeyboardHelpSection = new BasicActionsKeyboardHelpSection();
     super( {
       children: [ basicActionsKeyboardHelpSection ]
     } );
-
-    this.disposeHomeScreenKeyboardHelpContent = () => {
-      basicActionsKeyboardHelpSection.dispose();
-    };
-  }
-
-  public override dispose(): void {
-    this.disposeHomeScreenKeyboardHelpContent();
-    super.dispose();
   }
 }