x86/processor: Remove two unused function declarations

early_trap_init() and cpu_set_gdt() have been removed, so remove the stale
declarations as well.

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: keescook@chromium.org
Cc: luto@kernel.org
Cc: hpa@zytor.com
Cc: bp@suse.de
Cc: kirill.shutemov@linux.intel.com
Link: https://lkml.kernel.org/r/20180404064527.10562-1-douly.fnst@cn.fujitsu.com