audit: remove duplicate export of audit_enabled

audit_enabled has already been exported in include/linux/audit.h.  and
kernel/audit.h includes include/linux/audit.h, no need to export
aduit_enabled again in kernel/audit.h
Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/audit.h

@@ -60,7 +60,6 @@ struct audit_entry {
 };
 
 #ifdef CONFIG_AUDIT
-extern int audit_enabled;
 extern int audit_ever_enabled;
 #endif