staging: comedi: remove old auto-config

All the Comedi drivers that call `comedi_pci_auto_config()` or
`comedi_usb_auto_config()` define a `auto_attach()` handler in their
`struct comedi_driver`.  There is no need to fall back to abusing the
`attach()` handler any more, so remove the code that supports that.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>