x86/trap: Remove useless declaration

There is no early_trap_pf_init() implementation, hence remove this useless
declaration.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/1546591579-23502-1-git-send-email-kernelfans@gmail.com

arch/x86/include/asm/processor.h

@@ -742,7 +742,6 @@ enum idle_boot_override {IDLE_NO_OVERRIDE=0, IDLE_HALT, IDLE_NOMWAIT,
 extern void enable_sep_cpu(void);
 extern int sysenter_setup(void);
 
-void early_trap_pf_init(void);
 
 /* Defined in head.S */
 extern struct desc_ptr		early_gdt_descr;