refactor(@ngtools/webpack): remove unused transformation helper code

With the recent refactoring of the package's TypeScript transformers, several internal functions and types are no longer used or needed.

(cherry picked from commit bc0f329)

Author: clydin

packages/ngtools/webpack/src/transformers/ast_helpers.ts

@@ -5,8 +5,5 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-export * from './interfaces';
-export * from './ast_helpers';
-export * from './make_transform';
 export * from './elide_imports';
 export * from './replace_resources';