Drop obsolete btattach udev rule + systemd service
    
    Drop the obsolete udev rule + systemd service to call btattach on BT-HCIs
    connected via UART from userspace.
    
    I added these a long time ago to make BT work on Broadcom HCIs connected
    through an UART, but this has not been necessary for a long time.
    
    The kernel now makes the connection between the UART and the HCI itself
    and as part of this it no longer instantiates the platform-devices which
    the udev rule triggers on, so these have been a no-op for a long time now.