fixes #6856 - API v2 - more efficient import puppetclasses for single environment

`classes_env2` is not used, but remember the previous test failed without the stub since it was still being called. I left it in. Otherwise, the test seems meaningless as only `classes_env1` exists and therefore only `classes_env1` would appear whether an `environment_id` parameter was passed in the URL or not.  Does this make sense?