Convert remaining obuild packages to oasis and remove obuild from buildroot

[euanh]

The packages which are currently depend on obuild are:

• [x] ocaml-cdrom.spec
• [x] ocaml-netlink.spec
• [x] ocaml-qmp.spec
• [x] ocaml-xcp-inventory.spec
• [x] ocaml-xcp-rrd.spec
• [x] ocaml-xenops.spec
• [ ] sm-cli.spec
• [x] xcp-networkd.spec (repo contains an obuild file but it is not used)
• [x] xcp-rrdd.spec

[euanh]

Several packages only had vestigial dependencies on obuild.