ALSA: core: Remove unused snd_jack_set_parent

snd_jack_set_parent() was added as part of 2008's
commit e76d8cea ("ALSA: Add jack reporting API")

but hasn't been used.

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250502235219.1000429-6-linux@treblig.org