Legacy compatibility code

[Defenso-QTH]

iocage is full of backward compatibility code to run on older releases, with mentions going back to FreeBSD 9.3.

What would you think about removing these old parts of code, most of which could be considered like dirty hacks, I guess, to try and make the codebase easier to work with?

Note that the fact that some parts of the code mention such old releases does not provide any guarantee that it actually runs on said releases.

[dgeo]

This idea crossed my mind many times, I just miss time.
We could also drop some features, but I'm note sure which ones are really used...