Revert "seccomp: add a --no-seccomp option to disable dumping seccomp"

This reverts commit a98014f3.

As per Saied Kazemi, actually dump works without seccomp support
from the kernel on non-seccomped tasks. The only problem was with
criu check, but this would be addressed separately.

Reverting the commit not to burden the API with (yet) unneeded stuff.

Conflicts:
	lib/c/criu.h