Remove `AdjacencyList` from `diskann-providers`.

[hildebrandmw]

For historical reasons, diskann-providers has its own AdjacencyList from the early days. This has remained, largely because of its conversion from a byte slice is used in the disk index. It's functionality has been completely superseded by the AdjacencyList in diskann::graph. We just need a few updates to diskann-disk.

[hildebrandmw]

This will be closed by #915.

[hildebrandmw]

Closed by #915