Remove unused rules attribute in `RuleCollectorVisitor` in `parser_generator.py`

[chemelnucfin]

Bug report

Bug description:

I fixed a typo for the RuleCollectorVisitor class in gh-138208 and I thought that wouldn't require filing an issue. But since we are filing gh-138257 anyway, removing the attribute all together would be a better fix.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-138279: Remove unused attr in RuleCollectorVisitor in parser_generator.py #138280