[wiki] empty namespace pages

[tmomas]

@bobafetthotmail We have some empty namespage pages in the wiki. Can we delete them?

https://openwrt.org/docs/guide-user/firewall/shorewall/start
https://openwrt.org/docs/guide-user/firewall/netfilter-iptables/start
https://openwrt.org/docs/guide-user/firewall/fwbuilder/start
https://openwrt.org/docs/guide-user/firewall/firewall3/start
https://openwrt.org/docs/guide-user/firewall/firewall_concepts/start
https://openwrt.org/docs/guide-user/services/audio/start

[bobafetthotmail]

yeah they are left from the old firewall docs when I swapped the new ones in (the audio one is also another leftover, there is another audio namespace page already). I'll delete them too.