Remove unnecessary function call

Removes function call to `Datastore.kindByName()` since the the `KindDefinition` is already available. Also fixes an uncaught exception (seen when attempting to delete an `Entity`) since the kind itself was passed to `kindByName()` instead of the kind's name.

This was lightly tested using the same functionality I was using that failed, so hopefully this doesn't break anything else. Deleting an `Entity` now works, so that's promising.