FOR-SQUASH: Factor out with_conversion_script

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
FOR-SQUASH: Factor out reading of legacy qemu sig

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Remove xenguest/dumpcore from this tree

The OCaml version is now being built in ocaml-xen-lowlevel-libs. The C version
comes from our Xen patch queue.

The build for this component had already been disabled by c345a05.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>