No longer used (finally)
```
$ cd swh-environment
$ grep -r "BaseLoaderStorageTest" **/swh/*
Binary file swh-loader-core/swh/loader/core/tests/__pycache__/test_tests.cpython-37-pytest-5.4.3.pyc matches
Binary file swh-loader-core/swh/loader/core/tests/__pycache__/__init__.cpython-37-pytest-5.4.3.pyc matches
$ grep -r "BaseLoaderTest" **/swh/*
Binary file swh-loader-core/swh/loader/core/tests/__pycache__/test_tests.cpython-37-pytest-5.4.3.pyc matches
Binary file swh-loader-core/swh/loader/core/tests/__pycache__/__init__.cpython-37-pytest-5.4.3.pyc matches
```
Related to T2488