Remove unused import to get rid of eslint warning

This change was needed to create a subsequent commit that makes
modifications to this file. Without it, eslint would report an error
when trying to commit changes to actions.ts.

[MAILPOET-3885]

assets/js/src/form_editor/templates/store/actions.ts

@@ -1,5 +1,4 @@
 import { select } from '@wordpress/data';
-import MailPoet from 'mailpoet';
 
 import {
   CategoryActionType,