1. The preStart script ensures consistent ownership, even if the unbound
user's uid has changed
2. The unbound daemon does not generate data that needs to be private to
it, so it would not matter that a different service would end up
owning its data (as long as unbound remains enabled, it should reclaim
ownership soon enough anyway).
Thus, there's no clear benefit to allocate a dedicated uid for the
unbound service. This releases uid/gid 48.
Also, because the preStart script creates the data directory, there's no
need to specify a homedir or ask for its creation.