idle: remove cpu_idle() forward declarations

After all architectures were converted to the generic idle framework,
commit d190e8195b90 ("idle: Remove GENERIC_IDLE_LOOP config switch")
removed the last caller of cpu_idle(). The forward declarations in
header files were forgotten.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/cpu.h

···
 };
 
 void cpu_startup_entry(enum cpuhp_state state);
-void cpu_idle(void);
 
 void cpu_idle_poll_ctrl(bool enable);
 

include/linux/smp.h

···
 #include <linux/init.h>
 #include <linux/llist.h>
 
-extern void cpu_idle(void);
-
 typedef void (*smp_call_func_t)(void *info);
 struct call_single_data {
 	struct llist_node llist;