network: Drop any traces of ISDN

This has been removed a long time ago and we should probably spend a
little bit more time on keeping the networking code tidy :)

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

langs/pl/cgi-bin/pl.pl

@@ -912,7 +912,6 @@
 'hour-graph' => 'Godzina',
 'hours' => 'Godziny',
 'hours2' => 'Godziny',
-'ibod for dual isdn only' => 'iBOD can only be used with Dual ISDN.',
 'icmp selected but no type' => 'Wybrano protokół ICMP, ale nie określono typu ICMP.',
 'icmp type' => 'Typ ICMP',
 'id' => 'ID',
@@ -1038,10 +1037,6 @@
 'iptmangles' => 'IPTable Mangles',
 'iptnats' => 'IPTable Network Address Translation',
 'ipts' => 'iptables',
-'isdn' => 'ISDN',
-'isdn settings' => 'Dodatkowe ustawienia ISDN:',
-'isdn1' => 'Pojedynczy ISDN',
-'isdn2' => 'Podwójny ISDN',
 'january' => 'Styczeń',
 'javascript menu error1' => 'Jeżeli rozwijane menu nie działają poprawnie wyłącz javascript na',
 'javascript menu error2' => 'stronie.',