Make tests dependent on RocksDB unskippable

[dahlia]

Currently, tests dependent on RocksDB are skippable because too many tests fail if rocksdb.dll/librocksdb.so/librocksdb.dylib is unavailable. However, as Libplanet in itself virtually depends on RocksDb, skipping these tests is not substantial. Rather than skipping them, it probably is better to make RocksDB available on more platforms (see also https://github.com/planetarium/rocksdb-sharp/issues/10).

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.