The calls used old bugzilla URLs and nobody cared about that.
So apparently they are very unused.
There's also a potential conflict between gitlab and bugzilla URLs and
what base bug to use there.
The old usages have been converted to comments.
The tree is not needed to walk around the nodes.
It is however still needed for anything that requires modifying the
tree.
There is no immediate benefit in changing this API, but there might be
situations in the future where we can avoid looking up the tree when we
just want to check some details about the node.
