prometheus-node-exporter-lua: rewrite wifi scraper

prometheus-node-exporter-lua: rewrite wifi scraper

On my bullet m2, scrape duration goes from between 0.2 and 0.5 to a stable 0.025
We also don't depend on luci anymore

This remove wifi_network_up metric, but this metric was buggy
wifi_network_up{ifname="wlan0-1",ssid="test1",channel="11",mode="Master",bssid="12:34:56:78:9A:BC",country="FR",frequency="2.462"} 1
wifi_network_up{ifname="radio0.network2",ssid="test1",channel="11",mode="Master",country="US",frequency="2.462"} 0

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>