[yggdrasil-only] Drop non 0200::/7 connections

[d47081]

At this moment we have just replaced default Clearnet master in PR #5
As not everyone using Alfis DNS, additional PR #6 includes additional yggdrasil-only masters in the native format. Alfis DNS just useful for old builds on IP changes. I won't to include .ygg.at just because of Clearnet request.

What could be useful next for yggdrasil-only branch:

• By Sv downloadurl ipv6 #7
  • Default sv_downloadurl setting in server.cfg must check connections for IPv6 / 0200::/7 on client-side;
  • sv_downloadurl_ipv6 must check connections for 0200::/7
• Find and disable any other non-yggdrasil connections from engine