ALSA: usb-audio: scarlett2: Remove unused/useless code

Remove #define not used.
Remove useless assignments and copies.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/20210620164630.GA9180@m.b4.vu


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