OPENDJ-3148 Upgrade 2.6.4 -> 4.0.0: Error in logs after upgrading a replication topology

Some problems have already been fixed by the fix for OPENDJ-3149.

Another problem was due to trying to delete a now invalid objectClass definition
(unknown attribute type: ' ds-cfg-default-debug-level').
The fix consists in parsing only the OID rather than the whole objectClass definition.
Fixed this problem for all the following schema elements:
- attribute type OID
- object class OID
- name form OID
- DIT structure rule ruleID