Remove automated rpm and arch packaging.

Closes #6480.

This depends on a forthcoming website pr that adjusts the download page.
We are building Ubuntu packages on an Ubuntu build server. This is almost the same concept as a clean pbuilder environment. I think you can safely use `./configure`. I think that way we also have an internal test case for this script so we don't accidentally break it and packagers find out about it weeks after a release.