Remove no longer necessary WinCmdLineArgs class

This change removes one use case of `std::wstring_convert`, which is
deprecated in C++17 and removed in C++26. Other uses remain for now.

src/qt/bitcoin.cpp

@@ -478,11 +478,6 @@ static void SetupUIArgs(ArgsManager& argsman)
 
 int GuiMain(int argc, char* argv[])
 {
-#ifdef WIN32
-    common::WinCmdLineArgs winArgs;
-    std::tie(argc, argv) = winArgs.get();
-#endif
-
     std::unique_ptr<interfaces::Init> init = interfaces::MakeGuiInit(argc, argv);
 
     SetupEnvironment();