FWIW, I just did an install on a DigitalOcean droplet that does not have ipv6 configured and there is no problem.
Here’s this from an install from a couple days ago:
root@forum:~# grep ipv6 /etc/sysctl.conf
#net.ipv6.conf.all.forwarding=1
#net.ipv6.conf.all.accept_redirects = 0
#net.ipv6.conf.all.accept_source_route = 0
This stuff doesn’t’ hurt anything even though the droplet does not have ipv6 routed to it.