CP-10188: Package xentoollog as a top-level library

This pull request needs to be done in tandem with similar branches in ocaml-xen-lowlevel-libs and xen-api-libs-specs

https://github.com/xapi-project/ocaml-xen-lowlevel-libs/pull/73
https://github.com/xenserver/xen-api-libs-specs/pull/93
We've now got xenlight listed twice. I presume you meant one of these to be 'xentoollog', but we're probably getting that anyway as it's listed in xenlight's META file as a dependency. I believe we should only list things we directly depend upon, so we should just remove one of the xenlights.