fff-hoods/fff-wireless: Don't delete WiFi devices

We only want to remove WiFi interfaces, not devices during
reconfiguration. This still allows for complete reconfiguration,
but does not remove device attributes like a disabled 5 GHz or
similar.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Christian Dresel <fff@chrisi01.de>
Reviewed-by: Tim Niemeyer <tim@tn-x.org>