Remove redundant CWE link

Co-authored-by: Tony Torralba <[email protected]>

Author: egregius313

java/ql/src/Security/CWE/CWE-078/ExecTaintedEnvironment.qhelp

@@ -34,9 +34,6 @@ safe before using it.</p>
 <sample src="ExecTaintedEnvironmentChecked.java" />
 </example>
 <references>
-  <li>
-    MITRE: <a href="https://cwe.mitre.org/data/definitions/454.html">CWE-454: External Initialization of Trusted Variables or Data Stores</a>.
-  </li>
   <li>
     The Java Tutorials: <a href="https://docs.oracle.com/javase/tutorial/essential/environment/env.html">, Environment Variables</a>.
   </li>