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

[chemelnucfin]

I fixed a typo in this PR for thinking didn't need to file an issue. But since it did require an issue, a better fix would be to remove the attribute altogether.

[localhost cpython]$ git grep RuleCollectorVisitor
Tools/peg_generator/pegen/parser_generator.py:class RuleCollectorVisitor(GrammarVisitor):
Tools/peg_generator/pegen/parser_generator.py:        rule_collector = RuleCollectorVisitor(self.rules, self.callmakervisitor)

• Issue: Remove unused rules attribute in RuleCollectorVisitor in parser_generator.py #138279

[pablogsal]

LGTM

Great catch!