Revert pytest-xdist

[blrchen]

Description

This PR reverts pytest-xdist added by PR #773, with pytest-xdist, now ci tests fail with Different tests were collected between gw4 and gw5.

For more details please read: pytest-dev/pytest-xdist#432

After discussing with @loomlike , the root cause is in following code, NamedTemporaryFile().name confuses xdist. He will submit a right fix to mitigate this issue.

@pytest.mark.parametrize(
    "output_filepath", [None, NamedTemporaryFile().name],
)
def test__generate_config

How was this PR tested?

Does this PR introduce any user-facing changes?

• No. You can skip the rest of this section.
• Yes. Make sure to clarify your proposed changes.