Both snd_seq_prioq_remove_events() and snd_seq_prioq_leave() have a
very similar loop for removing events.  Unify them with a callback for
code simplification.

Only the code refactoring, and no functional changes.

Link: https://lore.kernel.org/r/20240222132152.29063-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>