ENGCOM-1901: [Forwardport] chore: remove unused less import #15921

 - Merge Pull Request magento/magento2#15921 from DanielRuf/magento2:2.3-develop-PR-port-15871
 - Merged commits:
   1. 4d03776

Author: magento-engcom-team

lib/web/css/docs/source/docs.less

@@ -21,7 +21,6 @@
 @import '_icons.less';
 @import '_loaders.less';
 @import '_messages.less';
-//@import 'navigation.less';
 @import '_layout.less';
 @import '_pages.less';
 @import '_popups.less';