Figure out what to do with the guardfraction feature

Guardfraction code is still around the codebase: guard_get_guardfraction_bandwidth(), should_apply_guardfraction(), routerstatus_parse_guardfraction(), guardfraction_line_apply(), guardfraction_file_parse_guard_line(), dirserv_read_guardfraction_file_from_str(), compute_weighted_bandwidths(). Also AFAIK some dirauths are still running the guardfraction python script.

Unfortunately, guardfraction code is still broken because of #16255 (moved) and possibly other unknown bugs. Hence, guardfraction support is disabled in the dirauths and all that code is currently useless.

My current plan here is to remove the guardfraction code from the Tor codebase, since fixing it and maintaining it as a PITA that I don't want to sign up for and we probably don't need it as much as we thought we did (see comment:36:ticket:16255).