Clear the subscription nag from Proxmox 5.2.x

This is from here:
https://gist.github.com/martin-juul/c4ac5c43c66452592597d894f1c9da2a

I applied this to 5.2-5 with no issues:
sed -i.bak 's/NotFound/Active/g' /usr/share/perl5/PVE/API2/Subscription.pm && systemctl restart pveproxy.service