Remove automated rpm and arch packaging.

Closes #6480.

This depends on a forthcoming website pr that adjusts the download page.
We do not otherwise include a complete Eluant.dll.config in the repo that is suitable for packaging.  We can't use `make dependencies` because the build server does not have lua installed.  Even if it did, this would be conceptually bogus: we are building a package targeting a specific client machine, and its state should not depend on the (potentially arbitrary) configuration of the build server.