[simple theme] SearXNG wordmark (plain SVG)

Remove XML namespaces from Incscape [1]::

   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"

[1] https://wiki.inkscape.org/wiki/PlainSVG



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>