DocumentRepository::find() when ID object also contains ID field name

[jmikola]

There appears to be logic DocumentRepository::find() to support passing a document as the $id parameter and unwrapping the identifier field value.

public function find($id, $lockMode = LockMode::NONE, $lockVersion = null)
{
    // ...

    /* TODO: What if the ID object has a field with the same name as the
     * class' mapped identifier field name?
     */
    if (is_array($id)) {
        list($identifierFieldName) = $this->class->getIdentifierFieldNames();

        if (isset($id[$identifierFieldName])) {
            $id = $id[$identifierFieldName];
        }

None of the tests in ODM depend on this functionality; however, some userland code may be. Consider removing this in 2.0.