IPC_HLE: Remove unused _Unimplemented_Device_ device

Unless I'm misreading the code, it doesn't look like this serves any
purpose, and is only polluting the logs.

_Unimplemented_Device_ looked like a device name that was picked to
be used somewhere else in Dolphin, but this doesn't seem to be the case
since 2012 (d95e31a removed the only other usage of this fake device).

Source/Core/Core/IPC_HLE/WII_IPC_HLE.cpp

@@ -164,7 +164,6 @@ void Reinit()
   AddDevice<CWII_IPC_HLE_Device_stub>("/dev/usb/hid");
 #endif
   AddDevice<CWII_IPC_HLE_Device_stub>("/dev/usb/oh1");
-  AddDevice<IWII_IPC_HLE_Device>("_Unimplemented_Device_");
 }
 
 void Init()