When fetching, the validation logic would prune a delegate if it was missing the
default branch. Originally, this was done to prevent any broken state, but later
it was realised that this can be too restrictive and would not allow nodes to
recover into an improved state.
Remove this check so thtat nodes can still fetch from each other when the
default branch is missing.
An e2e test is added to show that nodes can still fetch from each other and
still receive other references, even when a delegate is missing their default
branch.
eb095c109b