Drop support for local Update sites

[ferstl]

The --local-url was introduced to mirror remote update sites (repositories) to a local location and create Eclipse distros in a more reliable way. However, it turned out that this feature was rarely used. It should be removed to make the script a bit simpler.

[ferstl]

The remote-url config tag does not make much sense anymore. -> Deprecate it and rename it to url, repository-url or something more meaningful

[dnwe]

Is it worth documenting that you can use file:/// to point at local mirrors or extracted .zip updatesites?

[ferstl]

I'll mention it in the description of the configuration files