Class Based Components lesson fix for #29048

Class Based Components: 'Additional resources' points to article which do not
contain information on Class Based Components #29048. Removed additional resources link and replaced with
"It looks like this lesson doesn't have any additional resources yet. Help us expand this section by contributing to our curriculum."

react/class_components/class_based_components.md

@@ -286,4 +286,4 @@ The following questions are an opportunity to reflect on key topics in this less
 
 This section contains helpful links to related content. It isn't required, so consider it supplemental.
 
-- In general, the React documentation on [thinking in react](https://legacy.reactjs.org/docs/thinking-in-react.html) is a really good place to look into, if you want more practice with class-based components, from scratch.
+- It looks like this lesson doesn't have any additional resources yet. Help us expand this section by contributing to our curriculum.