gh-100546: Remove incorrect positional-only marker from eval (GH-100547)

All the arguments are positional-only.

The current status after GH-99476 seems to be to not use positional-only
markers in documentation, hence I've simply removed it.
(cherry picked from commit 71159a8e078bda0c9a39c6cd0980b7ba238dc582)

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>