Remove content from https://download.osgeo.org/pgrouting/

[dkastl]

I think we forgot to properly administrate some pgRouting related documents on https://download.osgeo.org/pgrouting/
This was used to provide files for download as well as a static copy of the previous TRAC-based website.

However, this seems to cause more issues than benefits:

• content is way too outdated and doesn't bring any benefit
• I saw some people referencing pgRouting from the old website even recently, which is not good
• there are not properly resolving links pointing to the old domain name, which is now used by a company

So I think we should take the whole content away from the OSGeo download folder, or at least make it inacessible.
However, I don't know anymore how to access.