Remove links to heap.space (#1954)

Author: jordikroon

get-involved.php

@@ -54,8 +54,6 @@
 
 <h3 class="content-title" id="references">Useful links for developers</h3>
 <ul class="content-box listed">
-    <li><a href="https://heap.space">lxr</a> - an online interface to the
-       PHP source, providing search facilities useful for programmers and researchers</li>
     <li><a href="https://wiki.php.net/rfc/howto">The RFC process</a> - the process
         by which developers can suggest and discuss new ideas with the community</li>
     <li><a href="/build-setup.php">Developer Setup Help</a> - some helpful information

sites.php

@@ -128,10 +128,6 @@ interface to it. There you can browse the history (and latest versions) of the
  the repository for the source code to the latest version of PHP itself.
  Checking out the source code can be done <a href="git.php">anonymously</a>.
 </p>
-<p>
- Using <a href="https://heap.space/">OpenGrok</a> is another option to view the
- source code, and it offers additional features like search and cross referencing.
-</p>
 </div>
 
 <h2 id="wiki" class="content-header"><a href="https://wiki.php.net/">wiki.php.net</a>: The PHP Wiki</h2>