pytest2/changelog/6909.bugfix.rst

Revert the change introduced by `#6330 <https://github.com/pytest-dev/pytest/pull/6330>`_, which required all arguments to ``@pytest.mark.parametrize`` to be explicitly defined in the function signature.

The intention of the original change was to remove what was expected to be an unintended/surprising behavior, but it turns out many people relied on it, so the restriction has been reverted.