revert: feat(dialog-base): add dismissHelper for visually-hidden buttons

we do not need to provide a close/visually hidden button for
non-dismissible dialogs

Author: marissahuysentruyt

packages/dialog/src/DialogBase.ts

@@ -194,23 +194,6 @@ export class DialogBase extends FocusVisiblePolyfillMixin(SpectrumElement) {
         super.update(changes);
     }
 
-    /**
-     * Returns a visually hidden dismiss button for mobile screen reader accessibility.
-     * This button is placed before and after dialog content to allow mobile screen reader
-     * users (particularly VoiceOver on iOS) to easily dismiss the overlay.
-     */
-    protected get dismissHelper(): TemplateResult {
-        return html`
-            <div class="visually-hidden">
-                <button
-                    tabindex="-1"
-                    aria-label="Dismiss"
-                    @click=${this.close}
-                ></button>
-            </div>
-        `;
-    }
-
     protected renderDialog(): TemplateResult {
         return html`
             <slot></slot>