This is a redesign from9b1f3cbc13where this was introduced. I deleted the AbstractConfig::toKeyValue since it was conspicuously and obviously broken for two years since450e5ec618. I asked myself if anyone was using it, given that it only emitted settings that were aliases (broken!), and found that nobody used it. The motivation for this change is the same for only emitting overridden settings to the protocol: the nix inside there may not be able to parse our defaults, as is the case of CppNix since the consensual accept-flake-config was added to Lix. Fixes: https://git.lix.systems/lix-project/lix/issues/739 Change-Id: Ib9874a52137f1f22220c25bcfa2425a4802509c7