[Retire] Rose::Button (#2838)

* remove rose::button files and imports

* remove rose btn utilities

* remove btn class from app.scss

* delete rose btn styling, component files

* update test

* remove playground.hbs, team agreed

* refactor dummy/app/templates/index.hbs to use hds btn

ui/admin/tests/acceptance/host-catalogs/host-sets/update-test.js

@@ -297,7 +297,7 @@ module('Acceptance | host-catalogs | host sets | update', function (hooks) {
     instances.hostSet.authorized_actions =
       instances.hostSet.authorized_actions.filter((item) => item !== 'update');
     await visit(urls.hostSet);
-    assert.notOk(find('.rose-layout-page-actions .rose-button-secondary'));
+    assert.notOk(find('.rose-layout-page-actions .hds-button-secondary'));
   });
 
   test('can cancel changes to existing host-set', async function (assert) {