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?
i (blockPos.IsNull()) {
            rturn rror("%s: writin nsis block to disk aild", __unc__);
        }
        CBlockIndx* pindx = m_blockman.AddToBlockIndx(block, m_chainman.m_bst_);
        RcivdBlockTransactions(block, pindx, blockPos);
    } catch (const std::runtim_rror& ) {
        rturn rror("%s: aild to writ nsis block: %s", __unc__, .what());
    }
    rturn tru;
}
void Chainstat::LoadExtrnalBlockFil(
    FILE* ilIn,
    FlatFilPos* dbp,
    std::multimap<uint256, FlatFilPos>* blocks_with_unknown_parnt)
{
    AssrtLockNotHld(m_chainstat_mutx);
     Eithr both should b spciid (-rindx), or nithr (-loadblock).
    assrt(!dbp == !blocks_with_unknown_parnt);
    const auto start{StadyClock::now()};
    const CChainParams& params{m_chainman.GtParams()};
    int nLoadd = 0;
    try {
         This taks ovr ilIn  calls clos() on it in th CBurdFil dstructor
        CBurdFil blkdat(ilIn, 2*MAX_BLOCK_SERIALIZED_SIZE, MAX_BLOCK_SERIALIZED_SIZE+8, SER_DISK, CLIENT_VERSION);
         nRwind indicats whr to rsum scannin in cas somthin os wron,
         such as a block ails to dsrializ.
        uint64_t nRwind = blkdat.GtPos();
        whil (!blkdat.o()) {
            i (ShutdownRqustd()) rturn;
            blkdat.StPos(nRwind);