Don't import/export from the same file twice (#5562)

Quiets down an annoying build warning in some configurations

Author: rictic

lib/utils/flush.js

@@ -11,8 +11,8 @@ import './boot.js';
 /* eslint-disable no-unused-vars */
 import { Debouncer } from '../utils/debounce.js';  // used in type annotations
 /* eslint-enable no-unused-vars */
-import { flushDebouncers } from '../utils/debounce.js';  // used in type annotations
-export { enqueueDebouncer } from '../utils/debounce.js';  // used in type annotations
+import {enqueueDebouncer, flushDebouncers} from '../utils/debounce.js';
+export {enqueueDebouncer};
 
 /**
  * Forces several classes of asynchronously queued tasks to flush: