Comment 9 for bug 1915712

I don't think we could/should warn because we don't know for sure which content slot should be used, just because the default-provider is disabled doesn't mean that the user isn't trying to use some other provider of the content interface.

We could maybe expose some additional property on interface slots which forces a warning to be exposed, but that would be a fair amount of work.

What would be easier and more preferable I think (that would also benefit more snaps) is to update the extension hook that is being used here to use `snapctl is-connected ...` on all the content interface plugs that should be coming from the platform snaps, that code if put into upstream snapcraft would benefit all snaps built with the extension that presumably all require using a platform snap.