infra: Remove broken discovery sites

Author: Bananeweizen

eclipsecs-sevntu-plugin-feature/feature.xml

@@ -15,8 +15,6 @@ Eclipse Public License - Version 1.0
    </license>
 
    <url>
-      <discovery label="Sources on GitHub" url="https://github.com/sevntu-checkstyle/sevntu.checkstyle"/>
-      <discovery label="SevNTU checks site" url="http://sevntu-checkstyle.github.io/sevntu.checkstyle/"/>
       <discovery label="Eclipse Update site" url="http://sevntu-checkstyle.github.io/sevntu.checkstyle/update-site/"/>
    </url>