Adapt to changes in `queryLedgerPeerSnapshot`
`queryLedgerPeerSnapshot` now returns `LedgerPeerSnapshot` directly instead of `Serialised (LedgerPeerSnapshot ...)`. Remove the `decodeLedgerPeerSnapshot` call and the error-handling path for decode failures. Also remove the now-unused `getShelleyNodeToClientVersion`, `conwayIndex`, `dijkstraIndex` functions and their associated imports (`ouroboros-consensus`, `sop-extras` from the cabal file).
