lufa:usb_usb: matrix_scan() is no longer needed

This is due to SOF timing fix of USB_Host_Shield_2.0.
The matrix_scan() was needed for usb_usb converter to recognize FC660C at startup.

tmk_core/protocol/lufa/lufa.c

@@ -661,7 +661,6 @@ int main(void)
 #else
         USB_USBTask();
 #endif
-        matrix_scan();
     }
     print("\nUSB configured.\n");