copy_signal() cleanup: clean tty_audit_fork()

Remove unneeded initialization in tty_audit_fork().  It is called only via
copy_signal() and is useless after the kmem_cache_zalloc() was used.

Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>