baselayout: replace cros-tmpfiles with systemd-tmpfiles

Reapply 7bc566630cb05d509371fa09435a08900057b308
ca-certificates: replace cros-tmpfiles with systemd-tmpfiles

Reapply 93ec181e26540e65f8b7636a6d63be87affb49a4
eclass: remove cros-tmpfiles.eclass, replaced by systemd-tmpfiles
Merge pull request #742 from marineam/cleanup

Cleanup custom tmpfiles code