refactor(cdk/bidi): remove unnecessary factory

Inlines a factory constant that doesn't need to be separate from its token definition.

Author: crisbeto

src/cdk/bidi/dir-document-token.ts

@@ -25,14 +25,5 @@ import {inject, InjectionToken, DOCUMENT} from '@angular/core';
  */
 export const DIR_DOCUMENT = new InjectionToken<Document>('cdk-dir-doc', {
   providedIn: 'root',
-  factory: DIR_DOCUMENT_FACTORY,
+  factory: () => inject(DOCUMENT),
 });
-
-/**
- * @docs-private
- * @deprecated No longer used, will be removed.
- * @breaking-change 21.0.0
- */
-export function DIR_DOCUMENT_FACTORY(): Document {
-  return inject(DOCUMENT);
-}