Remove NixNet DNS (#150)

These servers were shut down on September 10th. A notice has been on the webpage for a while as well: https://docs.nixnet.services/NixNet_DNS

_data/dns/nixnet.yml

@@ -1,26 +0,0 @@
-title: NixNet
-homepage: 'https://nixnet.xyz/'
-source: 'https://git.nixnet.xyz/NixNet/dns'
-anycast: true
-locations:
-  - US
-  - LU
-privacy_policy:
-  link: 'https://nixnet.xyz/privacy/'
-type:
-  name: Informal Collective
-  link: 'https://libreho.st/'
-  tooltip: >-
-    Part of LibreHosters,
-    "a network of cooperation and solidarity that uses free software to encourage decentralisation through federation and distributed platforms."
-logs:
-  policy: false
-protocols:
-  - name: DoH
-  - name: DoT
-dnssec: true
-qname_minimization: true
-filtering: Based on server choice
-providers:
-  - name: Frantech Solutions
-    link: 'https://frantech.ca/'