idle: remove cpu_idle() forward declarations

After all architectures were converted to the generic idle framework,
commit d190e8195b ("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 <geert+renesas@glider.be>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/cpu.h

@@ -256,7 +256,6 @@ enum cpuhp_state {
 };
 
 void cpu_startup_entry(enum cpuhp_state state);
-void cpu_idle(void);
 
 void cpu_idle_poll_ctrl(bool enable);
 

include/linux/smp.h

@@ -13,8 +13,6 @@
 #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;