r12880: Remove ldap partitions useless now and probably we

r12880: Remove ldap partitions useless now and probably we
will not use it anyway as we plan to support
partitions in ldb directly like with rootdse

Merge ldap_simple_ldb into ldap_backend, it is
not simple anymore and makes no sense to have
it separated now that ldap partitions are gone

Initial attempt at working to some limit to avoid DOSs
for the ldap server.

Simo.