Hotfix to ignore rules that existed in legacy parsers but not now

[dane-johnson]

Description

More effective guard against non-understood rules. Very temporary solution, these rules should never be able to exist in the first place

Motivation and Context

Closes maryvilledev/codesplain#97

Checklist:

• [x] My code follows the code style of this project.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

Browsers

• [ ] Chrome
• [x] Firefox
• [ ] Safari
• [ ] Mobile:
• [ ] Other:

Screenshots (if appropriate):

[smokinGun]

Please test in other browsers.