Improve generate_pyre_fixtures by removing get_rules_package_parser and integrate to the unified CLI

[jimmylai]

Improve generate_pyre_fixtures by removing get_rules_package_parser and integrate to the unified CLI.

1. get_rules_package_parser doesn't seem useful.
2. all CLI should be move to the new unified one for consistency and usability.

https://github.com/Instagram/Fixit/blob/6dc3b44df7eb558a25eaaf7a3c3314067ff13d59/fixit/common/generate_pyre_fixtures.py#L109