Adjust generated delete method

The delete method for Nodes will have the following schema:

```graphql
type Mutation {
  deleteMovies(where: MovieWhere): DeleteInfo!
}

type DeleteInfo {
  nodesDeleted: Int!
  relationshipsDeleted: Int!
}
```
Changes to the current implementation:

1. Return value is no longer the Deleted Entity
2. Multiple nodes can be deleted via the `where`-filter