Remove duped article from navigation listing

Author: bszyman

16/umbraco-cms/SUMMARY.md

@@ -188,7 +188,6 @@
       * [Workspace Context](customizing/extending-overview/extension-types/workspaces/workspace-context.md)
       * [Workspace Views](customizing/extending-overview/extension-types/workspaces/workspace-views.md)
       * [Workspace Footer Apps](customizing/extending-overview/extension-types/workspaces/workspace-footer-apps.md)
-  * [Extension Kind](customizing/extending-overview/extension-kind.md)
   * [Extension Conditions](customizing/extending-overview/extension-conditions.md)
   * [Custom Extension types](customizing/extending-overview/custom-extension-type.md)
 * [Foundation](customizing/foundation/README.md)