Currently we sort the APIs by path, in tidy.formatConfig. Do we definitely want the ordering of APIs to have no meaning?

The Python generation code currently uses the first path in the list for the default version, and I'm adding the option for an override - but I'm now wondering whether if I should require an override if there's more than one API, so that I'm not relying on ordering at all.

Likewise repometadata.FromLibrary uses the service config associated with the first API in the library.

If we can't rely on the ordering being preserved, I think we ought to document that really carefully.

Alternatively, let's get rid of the code that performs the sorting, and document that it won't be changed by tidying/formatting.