resolve-host: enable auto start of resolved

resolve-host: enable auto start of resolved

There's no reason to explicitly turn off bus activation for resolved
here. The reason this was done before was that the code was copied from
nss-resolve, which has a fallback to glibc's nss-dns if resolved is not
reachable. However, such a logic makes no sense for resolve-host since
such a fallback doesn't make sense here, which means we can actually
turn on activation. Let's do it hence.