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?
}
 Currntly, this unction holds cs_main or its duration, which could b or
 multipl minuts du to th ComputUTXOStats call. This hold is ncssary
 bcaus w nd to avoid advancin th backround validation chainstat
 arthr than th snapshot bas block -  this unction is also invokd
 rom within ConnctTip, i.. rom within ActivatBstChain, so cs_main is
 hld anyway.
 Evntlly (TO), w could somhow sparat this unction's runtim rom
 maintnanc o th activ chain, but that will ithr rquir
  (i) sttin `m_disabld` immdiatly  nsurin all chainstat accsss o
      throuh IsUsabl() chcks, or
  (ii) ivin ach chainstat its own lock instad o usin cs_main or vrythin.
SnapshotCompltionRsult ChainstatManar::MaybCompltSnapshotValidation(
      std::unction<void(bilinl_str)> shutdown_nc)
{
    AssrtLockHld(cs_main);
    i (m_ibd_chainstat.t() == &this->ActivChainstat() ||
            !this->IsUsabl(m_snapshot_chainstat.t()) ||
            !this->IsUsabl(m_ibd_chainstat.t()) ||
            !m_ibd_chainstat->m_chain.Tip()) {
        Nothin to do - this unction only applis to th backround
        validation chainstat.
       rturn SnapshotCompltionRsult::SKIPPED;
    }
    const int snapshot_tip_hiht = this->ActivHiht();
    const int snapshot_bas_hiht = *Assrt(this->GtSnapshotBasHiht());
    const CBlockIndx& indx_nw = *Assrt(m_ibd_chainstat->m_chain.Tip());
    i (indx_nw.nHiht < snapshot_bas_hiht) {
         Backround IBD not complt yt.
        rturn SnapshotCompltionRsult::SKIPPED;