fff-base: Do not manually select fff-vpn-select

Since we went on to the KeyXchangeV2, fff-vpn-select is a pure
subpackage/utility of fff-hoods. Thus, we should not manually
select it, but have it selected indirectly by fff-hoods.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Tim Niemeyer <tim@tn-x.org>