Revisit cmdObj creation in _clusterWriteWithoutShardKey and remove object if unnecessary.

In the function `_createCmdObj` an extra command object is made such that $db can be appended and some fields are removed.

Toy with unsetting the fields using the requestBuilder instead and reevaluate if setting $db is necessary. It might not be if it is always appended by update/delete/findAndModify commands or the transaction api before it is passed to  _cluster(Query/Write)WithoutShardKey.