tools/ocaml: Drop libxl and xentoollog bindings

tools/ocaml: Drop libxl and xentoollog bindings

There are significant issues with these bindings (they segfault for starters)
and their companion half in Xapi was deleted in 2018

  https://github.com/xapi-project/xen-api/commit/203292ebe0c487d7ae4adb961a6d080f4fbe933d

owing to there having been no development of these bindings since 2014.

In the unlikely event that we'd want to reinstate them, they'd need reworking
basically from scratch anyway.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>