Remove the 1.x projects that 2.0 does not build

AustinHarris.JsonRpc.Client, AustinHarris.JsonRpc.AspNet, JsonRpcTest and
TestClient were .NET Framework 4.0 packages.config projects outside the
solution. Nothing built them, CI never compiled them, and their pinned
Newtonsoft.Json 6.0.3 and 12.0.3 and Rx-Main 1.0 carried the repository's four
open security alerts. Their source stays in the history before 2.0; the README
and CHANGELOG say so.

Author: Astn