Old files should be removed after blocks are re-persisted

[afragapane]

After the most recent commit, the storage-audit seems to be accurate. However, there are still old, incorrect files lingering from the previous commit. You can see the issue in this directory: https://github.com/NeoResearch/neo-storage-audit/tree/master/BlockStorage_3700000 . The files with the commit message "Persisting Storage" use the incorrect version of neo-cli and have duplicate entries under files with the commit message "Persisting and Re-Persisting storage with neo 2.10.2 stable". For example, block 3601001 has an entry in file dump-block-3601001.json, and another entry in file dump-block-3602000.json.