Revert "Win32: Use the nicer looking blender-drawn confirmation message box when"

This reverts commit 60d6eb0b5d.

There is already a full patch (D3118) by brecht for this, will leave it up to him.

intern/ghost/intern/GHOST_SystemWin32.cpp

@@ -1751,3 +1751,9 @@ int GHOST_SystemWin32::toggleConsole(int action)
 
 	return m_consoleStatus;
 }
+
+int GHOST_SystemWin32::confirmQuit(GHOST_IWindow *window) const
+{
+	return (MessageBox(window ? ((GHOST_WindowWin32 *)window)->getHWND() : 0, "Some changes have not been saved.\nDo you really want to quit?",
+	                   "Exit Blender", MB_OKCANCEL | MB_ICONWARNING | MB_TOPMOST) == IDOK);
+}