None of these ship with the .NET Framework, they're a Mono-specific
artifact (either historically or deliberately):
cscompmgd.cs -> seems to have some types from Microsoft.CSharp, probably unused?
Microsoft.Web.Infrastructure.cs -> used for old ASP.NET MVC
SMDiagnostics.cs -> old .NET assembly we could probably remove
System.Json.cs -> JSON APIs from Silverlight
System.Json.Microsoft.cs -> same as above but with MS implementation
System.Net.Http.Formatting.cs -> used for old ASP.NET MVC
System.Numerics.Vectors.cs -> contains new Vector APIs, we added it as an assembly instead of facade
System.Reactive.Core.cs -> old copy of ReactiveX
System.Reactive.Debugger.cs -> old copy of ReactiveX
System.Reactive.Experimental.cs -> old copy of ReactiveX
System.Reactive.Interfaces.cs -> old copy of ReactiveX
System.Reactive.Linq.cs -> old copy of ReactiveX
System.Reactive.Observable.Aliases.cs -> old copy of ReactiveX
System.Reactive.PlatformServices.cs -> old copy of ReactiveX
System.Reactive.Providers.cs -> old copy of ReactiveX
System.Reactive.Runtime.Remoting.cs -> old copy of ReactiveX
System.Reactive.Windows.Forms.cs -> old copy of ReactiveX
System.Reactive.Windows.Threading.cs -> old copy of ReactiveX
System.Threading.Tasks.Dataflow.cs -> TPL Dataflow APIs that were distributed as NuGet only on netfx
System.Web.Http.cs -> used for old ASP.NET MVC
System.Web.Http.SelfHost.cs -> used for old ASP.NET MVC
System.Web.Http.WebHost.cs -> used for old ASP.NET MVC
System.Web.Mvc.cs -> used for old ASP.NET MVC
System.Web.Razor.cs -> used for old ASP.NET MVC
System.Web.WebPages.cs -> used for old ASP.NET MVC
System.Web.WebPages.Deployment.cs -> used for old ASP.NET MVC
System.Web.WebPages.Razor.cs -> used for old ASP.NET MVC
We can consolidate them into the mono folder.
