Remove `Type` from `config.Reference` struct

### What problem are you facing?

We now have `TerraformName` to represent the corresponding resource, hence `Type` is unnecessary and could be derived from `map[string]*config.Resource` map.

### How could Terrajet help solve your problem?

Make the existing `map[string]*config.Resource` map available to CRD builder so that it can look up the type name and write to file, hence remove the only usage of the `Type` field.