we currently have code dealing with falling back from InRelease
to Release{,.gpg} and it's all a bit much IMO. Now that buster
has been released with an InRelease file, the time has IMO come for
us to drop support for the old stuff from APT!
Timeline suggestion
-------------------
now add a warning to apt 1.9.x for repositories w/o InRelease,
but Release{,.gpg}
Aug/Sep turn the warning into an error, overridable with an option
(?)
Q1 2020 remove the code
My idea being that we give this a cycle in the Ubuntu 18.10 stable
release before we drop it, so people are ready for it.
Why remove it?
--------------
* It's annoying UX to have repositories with Release files and the
"Ign" lines
* Handling the fallback from InRelease to Release{,.gpg} involves some
abstractions
and logic and the less logic we have in security-relevant file
fetching, the better