plugins: remove usages of --experimental-type-build

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/proxy-backend/src/alpha.ts

@@ -26,7 +26,7 @@ import { createRouter } from './service/router';
  *
  * @alpha
  */
-export const proxyPlugin = createBackendPlugin({
+export default createBackendPlugin({
   pluginId: 'proxy',
   register(env) {
     env.registerInit({

plugins/proxy-backend/src/index.ts

@@ -21,4 +21,3 @@
  */
 
 export * from './service';
-export { proxyPlugin as default } from './plugin';