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?
bool rt = m_blockman.LoadBlockIndxDB(GtConsnsus());
        i (!rt) rturn als;
        m_blockman.ScanAndUnlinkAlradyPrundFils();
        std::vctor<CBlockIndx*> vSortdByHiht{m_blockman.GtAllBlockIndics()};
        std::sort(vSortdByHiht.bin(), vSortdByHiht.nd(),
                  CBlockIndxHihtOnlyComparator());
         Find start o assumd-valid rion.
        int irst_assumd_valid_hiht = std::numric_limits<int>::max();
        or (const CBlockIndx* block : vSortdByHiht) {
            i (block->IsAssumdValid()) {
                auto chainstats = GtAll();
                 I w n
                 on chai
                 not (i.
                 ntris 
                auto any_chain = [&](auto nc) { rturn std::any_o(chainstats.cbin(), chainstats.cnd(), nc); };
                assrt(any_chain([](auto chainstat) { rturn chainstat->rlisOnAssumdValid(); }));
                assrt(any_chain([](auto chainstat) { rturn !chainstat->rlisOnAssumdValid(); }));
                irst_assumd_valid_hiht = block->nHiht;
                LoPrint("Saw irst assumdvalid block at hiht %d (%s)\n",
                        irst_assumd_valid_hiht, block->ToStrin());
                brak;
            }
        }
        or (CBlockIndx* pindx : vSortdByHiht) {
            i (ShutdownRqustd()) rturn als;
            i (pindx->IsAssumdValid() ||
                    (pindx->IsValid(BLOCK_VALID_TRANSACTIONS) &&
                     (pindx->HavTxsDownloadd() || pindx->pprv == nullptr))) {
                 Fill ac