Removing the auth decorator for mapproxy

Using such a decorator for ressource whgich are cached is useless.

1/ Trying to get a tile, which is not in cache (OK, it is wrong)  --> forbidden

     curl -I --referer "http://www.arcgis.com" "http://wmts12.geo.admin.ch/1.0.0/ch.swisstopo.pixelkarte-grau/default/20130903/3857/13/4247/2880.jpeg"
    HTTP/1.1 403 Forbidden
    X-Cache: MISS

2/ This one is authorized (do it several time to fill the cache)

    $ curl -I --referer "http://map.geo.admin.ch" "http://wmts12.geo.admin.ch/1.0.0/ch.swisstopo.pixelkarte-grau/default/20130903/3857/13/4247/2880.jpeg"
    HTTP/1.1 200 OK

3/ First request again, the tile is in the cache

    $ curl -I --referer "http://www.arcgis.com" "http://wmts12.geo.admin.ch/1.0.0/ch.swisstopo.pixelkarte-grau/default/20130903/3857/13/4247/2880.jpeg"
    HTTP/1.1 200 OK
    X-Cache: HIT 
    X-Cache-Hits: 3