MarshallableEntryImpl should not eagerly unmarshall object key and values

The Object constructor for MarshallableEntryImpl eagerly marshalls the key, value, metadata and private metadata. This is not needed as this is used for load/publish purposes. If the store already provides the unmarshalled values, there is no reason for Infinispan to marshall them as it will store these in the storage format instead.
We should remove these lines https://github.com/infinispan/infinispan/blob/ed32d9055268d11b58ace243f1cba9044faaae87/core/src/main/java/org/infinispan/marshall/persistence/impl/MarshallableEntryImpl.java#L40-L42