REQUIREMENTS.html: XDR ref removed as it is included in libgis (trac https://trac.osgeo.org/grass/ticket/2236)

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@59854 15284696-431f-4ddb-bdfa-cd5b030d7da7

REQUIREMENTS.html

@@ -55,10 +55,6 @@ map formats<br>
 <a href="http://gdal.org">http://gdal.org</a>
 </li>
 
-<li><b>XDR</b> for raster I/O management (commonly provided on *NIX systems)<br>
-<a href="https://svn.r-project.org/R/trunk/src/extra/xdr">https://svn.r-project.org/R/trunk/src/extra/xdr</a>
-</li>
-
 </ul>
 
 <h3>Optional requirements:</h3>