Use the official JSON parser (#1151)

This remove Utf8son and JsonPrettyPrinter dependencies.

NOTE: the standard JSON parser doesn't support configurable
indentation, as a result, all the pretty printed JSON are indented with 2
spaces.

Ryujinx/Ui/AboutWindow.cs

@@ -1,11 +1,8 @@
 using Gtk;
 using System;
 using System.Diagnostics;
-using System.IO;
 using System.Reflection;
 using System.Runtime.InteropServices;
-using Utf8Json;
-using Utf8Json.Resolvers;
 
 using GUI = Gtk.Builder.ObjectAttribute;