Use upstream metaconfig tools rather than copies in the repository

[jmdh]

As demonstrated by the Debian package of perl, we can already use the separate metaconfig package (at least the version shipped in Debian) with essentially no change (currently there is one small reordering which we didn't track down the cause for).

Ideally we would not ship (or maintain versions of) the toolchain at all, and the Debian experience suggests that this is not a huge amount of work to achieve already.

This should probably something which only happens once the documentation review and update #15 has been completed, since that should make it easier to update the documentation in the confidence that it covers all of the use cases we care about.

The ticket would be resolvable when dist/ (other than dist/U) has been removed, as well as the files in bin/ which are derived from dist.