ALSA: aloop: Allocate resources with device-managed APIs

Use the new snd_devm_card_new() for the card object allocation, and
clean up the superfluous remove callback.

Link: https://lore.kernel.org/r/20210715075941.23332-78-tiwai@suse.de


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