docs: remove useless comment (#6159)

website/versioned_docs/version-2.0.0-beta.13/using-themes.md

@@ -245,27 +245,3 @@ These lifecycle methods are not essential but recommended:
 
 - [`validateThemeConfig({themeConfig, validate})`](./api/plugin-methods/static-methods.md#validateThemeConfig)
 - [`validateOptions({options, validate})`](./api/plugin-methods/static-methods.md#validateOptions)
-
-<!--
-
-Outline
----
-High-level overview about themes:
-- how to use a theme
-- how to pass theme configurations
-- how to swizzle components and the power of it
-
-Related pieces
----
-
-- [Advanced Guides – Themes](using-themes.md)
-- [Lifecycle APIs](./api/lifecycle-apis.md)
-
-References
----
-- [themes RFC](https://github.com/facebook/docusaurus/issues/1438)
-- [how classic template uses themes](/packages/docusaurus/templates/classic/docusaurus.config.js)
-- [using plugins doc](using-plugins.md)
-- [vuepress docs on themes](https://v1.vuepress.vuejs.org/theme/)
-
--->