GCAdapter: protect some more functions

Reset() and Setup() are not used outside of this namespace

Source/Core/InputCommon/GCAdapter_Null.cpp

@@ -9,9 +9,7 @@ namespace GCAdapter
 {
 
 void Init() {}
-void Reset() {}
 void ResetRumble() {}
-void Setup() {}
 void Shutdown() {}
 void SetAdapterCallback(std::function<void(void)> func) {}
 void StartScanThread() {}