Remove NuGet Gallery server entry

Author: Lamparter

nuget.config

@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
     <packageSources>
-        <add key="NuGet official package source" value="https://api.nuget.org/v3/index.json" />
         <add key="Local Packages" value="src/Files.App/nupkgs/" />
     </packageSources>
 </configuration>