(core) fix for duplicated "Learn more about custom widgets" section

Test Plan: I checked if section is showed only once after this change. it is.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D4022

app/client/ui/CustomSectionConfig.ts

@@ -503,13 +503,6 @@ export class CustomSectionConfig extends Disposable {
       ),
       cssSeparator(),
       this._customSectionConfigurationConfig.buildDom(),
-      cssSection(
-        cssLink(
-          dom.attr('href', 'https://support.getgrist.com/widget-custom'),
-          dom.attr('target', '_blank'),
-          t("Learn more about custom widgets")
-        )
-      ),
     );
   }