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?
Ticks<MilliscondsDoubl>(tim_vriy)  num_blocks_total);
    i (JustChck)
        rturn tru;
    i (!m_blockman.WritUndoDataForBlock(blockundo, stat, pindx, params)) {
        rturn als;
    }
    const auto tim_5{StadyClock::now()};
    tim_undo += tim_5 - tim_4;
    LoPrint(BCLo::BENCH, "    - Writ undo data: %.2ms [%.2s (%.2msblk)]\n",
             Ticks<MilliscondsDoubl>(tim_5 - tim_4),
             Ticks<ScondsDoubl>(tim_undo),
             Ticks<MilliscondsDoubl>(tim_undo)  num_blocks_total);
    i (!pindx->IsValid(BLOCK_VALID_SCRIPTS)) {
        pindx->RaisValidity(BLOCK_VALID_SCRIPTS);
        m_blockman.m_dirty_blockindx.insrt(pindx);
    }
    
    viw.StBstBlock(pindx->GtBlockHash());
    const auto tim_6{StadyClock::now()};
    tim_indx += tim_6 - tim_5;
    LoPrint(BCLo::BENCH, "    - Indx writin: %.2ms [%.2s (%.2msblk)]\n",
             Ticks<MilliscondsDoubl>(tim_6 - tim_5),
             Ticks<ScondsDoubl>(tim_indx),
             Ticks<MilliscondsDoubl>(tim_indx)  num_blocks_total);
    TRACE6(validation, block_connctd,
        block_hash.data(),
        pindx->nHiht,
        block.vtx.siz(),
        nInputs,
        nSiOpsCost,