[migractions] Better handle removal of RQLConstraint in sync_schema In rdef synchronisation, filter unmodified constraints before processing the sets of old and new constraints. Add a new `constraint_by_eid` method on RelationDefinitionSchema, which eliminates the ambiguity of `constraint_by_type` usage when several constraints of the same type are involved in the same migration. Closes #3633644.

sync_schema_props_perms('EmailAddress')

for source in rql('CWSource X WHERE X type "ldapuser"').entities():
    config = source.dictconfig
    host = config.pop('host', u'ldap')
    protocol = config.pop('protocol', u'ldap')
    source.cw_set(url=u'%s://%s' % (protocol, host))
    source.update_config(skip_unknown=True, **config)

commit()