Update sqlserver.html

Author: JacobReynolds

misc/sandboxes/sqlserver.html

@@ -3,5 +3,4 @@ <h3 id="sandboxes">Sandboxes</h3>
 <p>Some useful online sandboxes for testing queries can be found below: <br>
     <a rel="noopener" target="_blank" href="http://sqlfiddle.com/#!6">http://sqlfiddle.com/</a> <br>
     <a rel="noopener" target="_blank" href="https://turbo.net/sql">https://turbo.net/sql</a> <br>
-    <a rel="noopener" target="_blank" href="https://sqlzoo.net/">https://sqlzoo.net/</a> <br>
-    <a rel="noopener" target="_blank" href="http://www.headfirstlabs.com/sql_hands_on/">http://www.headfirstlabs.com/sql_hands_on/</a></p>
+    <a rel="noopener" target="_blank" href="https://sqlzoo.net/">https://sqlzoo.net/</a></p>