src: remove Doxygen header if not API

src/knot/nameserver/chaos.h

src/knot/updates/acl.h

src/knot/updates/ddns.h

src/knot/zone/contents.h

src/knot/zone/zone-dump.h

src/utils/common/exec.h

src/utils/common/hex.h

src/utils/common/lookup.h

src/utils/common/msg.h

src/utils/common/netio.h

src/utils/common/params.h

src/utils/common/resolv.h

src/utils/common/token.h