drop legacy support: stop supporting oldstable and older

[adrelanos]

#266 is one example of something difficult to implement due to old version support. That is versions older than Debian stable. Speak stable -1 (oldstable) or stable -2 (oldoldstable) or even older.

Legacy support is expensive.

Unless there is a specific reason to support anything older than stable, I would suggest to deprecate support for it. I would not know why I would want to use a recent version of grml-debootstrap to build an oldstable or older version of Debian.

If legacy support was dropped, then the source code could be simplified.

If this is a popular feature request that you wish to adhere or if you need it for some of your own purposes, that would be of course fine.

Sometimes behavior slips into a project, is then carried forward without anyone still knowing why this is the case while it might no longer be necessary. At the chance that this might be happening here, suggesting this.

[zeha]

Hi @adrelanos,

both @mika and me regularly use grml-debootstrap to boot older Debian versions.

I agree that it's a pain to support older versions, but I think we should keep the support.

From my PoV at least for buster. I think @mika also cares about jessie.

[mika]

Thanks for raising this, @adrelanos.

I agree that we should avoid having support for older Debian releases at all costs. I'm a fan of backwards and forwards compatibility, but also this has its limits and given that we have CI tests in grml-debootstrap, it makes sense to keep the build/test matrix somewhat sane(r). 8-)

So yeah, I would consider supporting releases until buster as well, and drop older releases.
Further opinions?