Licence fix, add SPDX-License-Identifier, remove unused code files

src/rig/RigThread.cpp

@@ -1,3 +1,6 @@
+// Copyright (c) Charles J. Cliffe
+// SPDX-License-Identifier: GPL-2.0+
+
 #include "RigThread.h"
 
 std::vector<const struct rig_caps *> RigThread::rigCaps;

src/rig/RigThread.h

@@ -1,3 +1,6 @@
+// Copyright (c) Charles J. Cliffe
+// SPDX-License-Identifier: GPL-2.0+
+
 #pragma once
 
 #include "IOThread.h"