A word of warning, removing the DNS entry only prevents name
resolution (converting a URL to a IP address). If someone (or
something) uses an IP address to access the Web, it would still work.
It depends on if this gives you what you need.
However the default route is the route an IP stack goes to if the
destination address is not on the local net. If you take this away,
the PC can not get outside the local network (with either URL or IP
address).
Of course a technical person could work this out & put it back,
therefore if security is a requirement, block it at the firewall router.