Remove ad2oLschema, insted call it directly from provision-backend

Remove ad2oLschema, insted call it directly from provision-backend

This removes a level of indirection via external binaries in the
provision-backend code, and also makes better use of our internal code
for loading schema from an LDIF file.

Remaining to do: Sort the output again, as the load from LDIF is
unsorted (also needed because the normal LDB load from sorted input is too slow
anyway, and is only needed here).

Andrew Bartlett