ALSA: xen-front: remove unused struct 'alsa_sndif_hw_param'

'alsa_sndif_hw_param' has been unused since the original
commit 1cee5593 ("ALSA: xen-front: Implement ALSA virtual sound
driver").

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://lore.kernel.org/r/20240601232604.198662-1-linux@treblig.org


Signed-off-by: Takashi Iwai <tiwai@suse.de>