Use positional argument for input files in 2john scripts

[exploide]

As requested in #5643 (comment) this PR turns the input file arguments for radius2john.py and aix2john.py into positional arguments.

Plus a bit of cleanup while I was at it.

[magnumripper]

Thanks! I see radius2john also takes pcap so presumedly the reason for it not being a part of pcap2john is the potential need for -l and -p.

I tested radius2john with our samples, we don't seem to have any samples for AIX.

[exploide]

we don't seem to have any samples for AIX.

The only bit I found was in the comment at the beginning of the script. I copied that to a file and the script produced the same output on it.