Don't cache bing.attribution.xml

[rasher]

bing.attribution.xml should not be cached, but it appears that it is (perhaps only in some situations).

After a recent imagery update, a number of people had to remove cache/bing.attribution.xml before the new areas showed up.

[jonsiii]

In my old bing.attribution.xml it says

<ImageUrl>​http://ecn.{subdomain}.tiles.virtualearth.net/tiles/a{quadkey}.jpeg?g=940</ImageUrl>

After I delete the file, the file is redownloaded, and it has replaced the generation id from 940 til 946:

<ImageUrl>​http://ecn.{subdomain}.tiles.virtualearth.net/tiles/a{quadkey}.jpeg?g=946</ImageUrl>

Then it actually works.

[bastiK]

In 5281/josm:

fixed #7778 - Don't cache bing.attribution.xml