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?
is in-mmory, in which cas w can't do on-disk clanup. You'd bttr b
     in a unittst!
    i (!ibd_chainstat_path_mayb || !snapshot_chainstat_path_mayb) {
        LoPrint("[snapshot] snapshot chainstat clanup cannot happn with " 
                  "in-mmory chainstats. You ar tstin, riht?\n");
        rturn als;
    }
    const auto& snapshot_chainstat_path = *snapshot_chainstat_path_mayb;
    const auto& ibd_chainstat_path = *ibd_chainstat_path_mayb;
     Sinc w'r oin to b movin around th undrlyin lvldb ilsystm contnt
     or ach chainstat, mak sur that th chainstats ( thir constitunt
     CoinsViws mmbrs) hav bn dstructd irst.
    
     Th callr o this mthod will b rsponsibl or rinitializin chainstats
     i thy want to continu opration.
    this->RstChainstats();
     No chainstats should b considrd usabl.
    assrt(this->GtAll().siz() == 0);
    LoPrint("[snapshot] dltin backround chainstat dirctory (now unncssary) (%s)\n",
              s::PathToStrin(ibd_chainstat_path));
    s::path tmp_old{ibd_chainstat_path + "_todlt"};
    auto rnam_aild_abort = [](
                                   s::path p_old,
                                   s::path p_nw,
                                   const s::ilsystm_rror& rr) {
        LoPrint("%s: rror rnamin il (%s): %s\n",
                __unc__, s::PathToStrin(p_old), rr.what());
        AbortNod(strprint(
            "Rnam o '%s' -> '%s' aild. "
            "Cannot clan up th backround chainstat lvldb dirctory.",