ALSA: pcm: Drop obsoleted PCM copy_user and copy_kernel ops

Finally all users have been converted to the new PCM copy ops, let's
drop the obsoleted copy_kernel and copy_user ops completely.

Link: https://lore.kernel.org/r/20230815190136.8987-26-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>