ALSA: gus: Remove unused declarations

snd_gf1_synth_init() and snd_gf1_synth_done() were declared but never
implenmented and used since the beginning of kernel git history.

Signed-off-by: Yue Haibing <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

sound/isa/gus/gus_reset.c

···
 #include <sound/core.h>
 #include <sound/gus.h>
 
-extern int snd_gf1_synth_init(struct snd_gus_card * gus);
-extern void snd_gf1_synth_done(struct snd_gus_card * gus);
-
 /*
  *  ok.. default interrupt handlers...
  */