Drop unneeded code to simplify getting hosts over ubus

This code in umdns_hosts was there since ever but it seems like an
unneeded copy & paste part of umdns_browse. In this function we iterate
over *host* entries of cached services list. It means the entry field
conains values like "example.local".

In such case looking for "._" is pointless and appending ".local"
results in looking for entries like "example.local.local".

This code make sense for browsing *services* only where for entries like
"ex._ssh._tcp.local" we try dumping "ex.local" & "ex._ssh._tcp.local".

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>