fix: remove broken link Lernen from map view

The linked page `/lernen.html` does not exist, the map view is linked
directly from the main page, therefor having something in breadcrumb
navigation does not seem necessary.

templates/html/kurse-karte.html

@@ -8,7 +8,6 @@
       <nav aria-label="breadcrumb">
         <ol class="breadcrumb">
           <li class="breadcrumb-item"><a href="index.html">Home</a></li>
-          <li class="breadcrumb-item"><a href="lernen.html">Lernen</a></li>
           <li class="breadcrumb-item active" aria-current="page">Kurse vor Ort</li>
         </ol>
       </nav>
@@ -50,4 +49,4 @@
       </div>
       
     </div>
-</div>
+</div>