Remove auto-index from LINK property, as the code doesn't set the OClass of the linked schema
when creating the property. The missing linked OClass results in a OCommandExecutionException
in `OChainedIndexProxy.prepareLastIndexVariants` when you try to use the index in 2.0-M3.

AFAICT previously in 2.0-M2 this situation was silently being ignored and the index never used.

git bisect suggests https://github.com/orientechnologies/orientdb/commit/fae55b4 introduced the
change in behaviour, which then revealed this missing OClass for the indexed LINK property.