Remove mentions of community Slack (#79)

Author: nginx-jack

layouts/index.html

@@ -189,13 +189,6 @@ <h3 class="saas-title">NGINX Unit</h3>
              </div>
           </div>
        </div>
-       <div class="container-fluid col-xl-12" id="community-alert">
-         <div class="row justify-content-center">
-             <div class="alert alert-light" role="alert">
-                 <p class="card-title" style="font-weight: 400;">Join the <a href="https://community.nginx.org/joinslack" alt="NGINX Community Slack">NGINX Community Slack</a> to ask and answer questions, discuss NGINX, and share useful advice and resources.</p>
-             </div>
-         </div>
-     </div>
     </section>
  </div>