Change the DI Microsoft to use 'RemoveOrUpdate` when it becomes available

[glennawatson]

if list empty remove contract entirely

splat/src/Splat.Microsoft.Extensions.DependencyInjection/MicrosoftDependencyResolver.cs

Lines 327 to 332 in 5c73294

	// TODO if list empty remove contract entirely
	// need to find how to atomically update or remove
	// https://github.com/dotnet/corefx/issues/24246
	return list;
	});
	}

---

This comment was generated by todo based on a TODO comment in 5c73294 in #370. cc @weitzhandler.

Originally posted by @todo in #370 (comment)

[glennawatson]

We are waiting on https://github.com/dotnet/corefx/issues/24246