location-importer.in: delete 6to4 IPv6 space as well

2002::/16 is an anycast prefix for 6to4 scenarios, as specified in RFC
3068. We currently process an announcement from Hurricane Electric for
it, and since it is an anycast network, multiple entities across the
world announce it as well.

Thereof, it does not make sense to include it in the database - as of
today, we do not have a country for it, either.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>