Documentation: remove the linker command line switch --static from the final step described in the cross-compilation guide

Static linking of the binary criu isn't supported any more.

Reported-by: riya khanna <riyakhanna1983@gmail.com>
Signed-off-by: Alexander Kartashov <alekskartashov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>