nav: Removed Wiki

It did not fit in the header after adding the "Event WLAN".

Also: There are so little changes. Having it "for reference"
in the footer seems enough.

includes/nav

@@ -20,9 +20,6 @@
         <a href="/event.html">Event WLAN</a>
         </li>
         <li>
-        <a href="//wiki.freifunk-bs.de/">Wiki</a>
-        </li>
-        <li>
         <a href="https://stratum0.org/blog/categories/freifunk/">Blog</a>
         </li>
         <li>