tracehook: unexport ptrace_notify

The ptrace_notify() function should not be called by any modules.  It was
only ever exported to be called by binfmt exec functions.  But that is no
longer necessary since fs/exec.c deals with that generically now.  There
should be no calls to ptrace_notify() from outside the core kernel.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>