parasite, restorer: Cleanup ld scripts

There is no need for specific parasite or restorer
head sections, a general "head" one is enough.

Also .stack section is dropped since it's never used.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>