parasite: Get rid of redundant PTRACE_INTERRUPT/PTRACE_CONT tail

The tail PTRACE_INTERRUPT/PTRACE_CONT call in parasite calling code
is redundant as far as I can say, thus get rid of it.

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