Always use configured root when installing WAD

This prevents Dolphin from writing to /sys/uid.sys (on the host; root
partition) when installing a WAD before starting emulation, because
the session root is not initialized at that moment.

Incidentally, this also gets rid of a singleton.

Source/Core/Core/HW/HW.cpp

@@ -52,7 +52,6 @@ void Init()
   if (SConfig::GetInstance().bWii)
   {
     Core::InitializeWiiRoot(Core::g_want_determinism);
-    DiscIO::cUIDsys::AccessInstance().UpdateLocation();
     DiscIO::CSharedContent::AccessInstance().UpdateLocation();
     IOS::Init();
     IOS::HLE::Init();  // Depends on Memory