x86: remove duplicate start_kernel declaration

start_kernel is already declared in a generic header file.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/head64.c

@@ -10,6 +10,7 @@
 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/percpu.h>
+#include <linux/start_kernel.h>
 
 #include <asm/processor.h>
 #include <asm/proto.h>

include/asm-x86/proto.h

@@ -8,8 +8,6 @@
 struct cpuinfo_x86; 
 struct pt_regs;
 
-extern void start_kernel(void);
-
 extern void early_idt_handler(void);
 
 extern void init_memory_mapping(unsigned long start, unsigned long end);