ALSA: firewire-digi00x: remove transaction handler for unknown purpose

For digi00x series, asynchronous transaction is not used to transfer MIDI
messages to/from control surface. One of transction handlers in my previous
work loses its practical meaning.

This commit removes the handler. I note that unit of console type
transfers 0x00001000 to registered address of host space when switching
to 'standalone' mode. Then the unit generates bus reset.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>