The port override feature of network.config is hard to maintain, since
changes to devices (e.g. port configuration updates, switch to DSA) have
to be applied to this manual override as well.
As this feature is probably hardly used anyway, remove it.
The port override migration for the Archer C7 v2 is not necessary
anymore, remove it as well.
Signed-off-by: Fabian Bläse <fabian@blaese.de>