parasite-syscall: cure task without parasite with unmap

In case of `criu exec`, we do not insert parasite daemon inside task.
So, we don't have the daemon which could unmap itself and by that
reason, we should unmap remote_map with hands (raw syscall).

Cc: Andrew Vagin <avagin@virtuozzo.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>