Changes

{osmo-dev-on-,}debian-sid: remove

I just discovered this while updating the remaining users of legacy
git.osmocom.org. These containers have been added in 2017 and don't
build anymore, let's remove them. I highly doubt anybody is still these,
and if they do, we can bring them back easily.

Change-Id: I379d56676327a59962d955bb3d4a0562142228e3