removing link to obsolete doc

README.md

@@ -11,9 +11,6 @@ The explainer is organized as follows:
 
 * What are the problems being solved/ different modes of fenced frames?
    * [Modes/Use cases of fenced frames](https://github.com/WICG/fenced-frame/blob/master/explainer/use_cases.md)
-
-* Deep dive in the "opaque-ads" use case which will be the first launch of fenced frames
-   * [Opaque ads use cases](https://github.com/WICG/fenced-frame/blob/master/explainer/opaque_ads_use_cases.md)
 
 * How fenced frames integrates with the web platform. This is a growing list of things and will be added to the documentation
    *  [Integration with the web platform](https://github.com/WICG/fenced-frame/blob/master/explainer/integration_with_web_platform.md)