Make FetchUselessDescriptors fetch all consensus flavours
FetchUselessDescriptors 1 used to imply
UseMicrodescriptors 0, but due to legacy/trac#6769 (moved), it doesn't in 0.3.0 and later.
Therefore, clients that want to download a full consensus have to explictly set
We should document this in the man page and probably the changelog summary, as it is a breaking change for many configs that used to obtain a full consensus. (Alternately, we could fix this bug by FetchUselessDescriptors download a full consensus, even on clients, and document that behaviour.)
Discovered when running a test bandwidth authority - see legacy/trac#20621 (moved).