luci-mod-network: don't hide "Device" on protocol change

Device ("ifname" UCI option) doesn't depend on protocol so there is no
need to hide / reset it on protocol change.

While at it drop names of two removed inputs (dead code).

Fixes: ec020cee

 ("luci-mod-network: drop support for *editing* legacy bridges")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>