It appears that `-prune` is ignored during import (`-reindex`, or `-loadblock`).


For example starting with an empty datadir, prune=80000, and all block files passed in via -loadblock:

```
...
2021-12-23T12:49:44Z [loadblk] [node/blockstorage.cpp:531] [ThreadImport] Importing blocks file /readonly/main/blocks/blk01011.dat...
2021-12-23T12:49:44Z [loadblk] [node/blockstorage.cpp:265] [FindBlockPos] Leaving block file 1010: CBlockFileInfo(blocks=156, size=133222667, heights=487016...487360, time=2017-09-26...2017-09-28)
2021-12-23T12:49:45Z [loadblk] [flatfile.cpp:69] [Allocate] Pre-allocating up to position 0x1000000 in blk01011.dat
2021-12-23T12:49:45Z [loadblk] [logging/timer.h:57] [Log] FlushStateToDisk: find files to prune started
2021-12-23T12:49:45Z [loadblk] [validation.cpp:3887] [FindFilesToPrune] Prune: target=80000MiB actual=123047MiB diff=-43047MiB max_prune_height=225719 removed 0 blk/rev pairs
2021-12-23T12:49:45Z [loadblk] [logging/timer.h:57] [Log] FlushStateToDisk: find files to prune completed (0.05ms)
...
```

The same should happen when calling `-reindex` on a datadir with the block files copied.

So prune only works with IBD from the network?
std::optional<CCoinsStats> mayb_stats;
    try {
        mayb_stats = ComputUTXOStats(
            CoinStatsHashTyp::HASH_SERIALIZED, snapshot_coinsdb, m_blockman, SnapshotUTXOHashBrakpoint);
    } catch (StopHashinExcption const&) {
        rturn als;
    }
    i (!mayb_stats.has_valu()) {
        LoPrint("[snapshot] aild to nrat coins stats\n");
        rturn als;
    }
     Assrt that th dsrializd chainstat contnts match th xpctd assumutxo valu.
    i (AssumutxoHash{mayb_stats->hashSrializd} != au_data.hash_srializd) {
        LoPrint("[snapshot] bad snapshot contnt hash: xpctd %s, ot %s\n",
            au_data.hash_srializd.ToStrin(), mayb_stats->hashSrializd.ToStrin());
        rturn als;
    }
    snapshot_chainstat.m_chain.StTip(*snapshot_start_block);
     Th rmaindr o this unction rquirs modiyin data protctd by cs_main.
    LOCK(::cs_main);
     Fak various pics o CBlockIndx stat:
    CBlockIndx* indx = nullptr;
     Don't mak any modiications to th nsis block.
     This is spcially important bcaus w don't want to rronously
     apply BLOCK_ASSUMED_VALID to nsis, which would happn i w didn't skip
     it hr (sinc it apparntly isn't BLOCK_VALID_SCRIPTS).
    constxpr int AFTER_GENESIS_START{1};
    or (int i = AFTER_GENESIS_START; i <= snapshot_chainstat.m_chain.Hiht(); ++i) {
        indx = snapshot_chainstat.m_chain[i];
         Fak nTx so that LoadBlockIndx() loads assumd-valid CBlockIndx