____call_usermodehelper: don't flush_signals()

____call_usermodehelper() has no reason for flush_signals().  It is a fresh
forked process which is going to exec a user-space application or exit on
failure.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>