Get rid of `IStateStore.PruneStates()` method & `MerkleTrie.IterateHashNodes()` method

[moreal]

📔 Overview

Currently, there are IStateStore.PruneStates()(TrieStateStore.PruneStates()) method and MerkleTrie.IterateHashNodes() method. And TrieStateStore.PruneStates()' implementation is very inefficient so #1691 introduced TrieStateStore.CopyStates() and libplanet should suggest efficient way and deprecate inefficient way.

🤔 Furthermore

While I had worked for #1691, I felt confused about IStateStore's role. Currently, there is only IStateStore.GetStateRoot() method and it just returns MerkleTrie with IKeyValueStore, secure bool option received from its constructor. it doesn't do anything except for it. Historically, IStateStore was introduced to replace state stores based on state-reference smoothly. But, today, IStateStore seems useless because Libplanet is using MPT as blockchain protocol level and I believe it will not be replaced, at least in near days.

References

See also https://github.com/planetarium/libplanet/pull/1691#issuecomment-1018113164.

[stale[bot]]

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