dependencies in requirements.txt not present in top level

See the test [here](https://github.com/nexB/scancode-toolkit/tree/develop/tests/packagedcode/data/pypi/source-package) for which [top-level dependencies](https://github.com/nexB/scancode-toolkit/blob/develop/tests/packagedcode/data/pypi/source-package/pip-22.0.4-pypi-package-expected.json#L2) doesn't contain the requirements that are present in this [package_data dependencies](https://github.com/nexB/scancode-toolkit/blob/develop/tests/packagedcode/data/pypi/source-package/pip-22.0.4-pypi-package-expected.json#L235)

This was probably introduced [here](https://github.com/nexB/scancode-toolkit/commit/a13f81e8a2a9902b565583a3dfc8c3a509135546#diff-80126c7a092bbabab590e68c600239f669e58ca6f8f3f469add6cede74258ffa)