Replace Redpoint.AutoDiscovery implementation with native C#

[hach-que]

Currently Redpoint.AutoDiscovery uses the native operating system's DNS-SD APIs, such as DnsServiceConstructInstance. However, this makes it awkward to build UET on other platforms because we're not just consuming this library as a NuGet package; it is part of the build process.

In theory we can replace the P/Invoke dependencies with a native C# implementation (see https://github.com/kendolondon/DnsSDNet/blob/master/Source/UnicastDnsSDRegistrator.cs). Unfortunately DNS-SD is poorly documented and there isn't a straight-forward example of "register a single service", so implementing this probably involves a lot of trial and error to get it working correctly.

Alternatively, the only thing that is actually using Redpoint.AutoDiscovery at the moment is the "run remote" command, which is intended for doing things like testing packaged Windows builds on remote machines while still having the desktop/graphics rendering that SSH would not provide. It used to be used for OpenGE, but that got removed once UBA was available. I'm no longer using the "run remote" command internally, so we could just remove Redpoint.AutoDiscovery entirely and call it a day.