panic: make print_oops_end_marker() static

Since print_oops_end_marker() is not used externally, also remove it in
kernel.h at the same time.

Signed-off-by: Yue Hu <huyue2@yulong.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/20200724011516.12756-1-zbestahu@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/panic.c

@@ -551,7 +551,7 @@ static int init_oops_id(void)
 }
 late_initcall(init_oops_id);
 
-void print_oops_end_marker(void)
+static void print_oops_end_marker(void)
 {
 	init_oops_id();
 	pr_warn("---[ end trace %016llx ]---\n", (unsigned long long)oops_id);