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?
m_bst_invalid = pindx;
            }
            i (pindx->IsValid(BLOCK_VALID_TREE) && (m_bst_ == nullptr || CBlockIndxWorkComparator()(m_bst_, pindx)))
                m_bst_ = pindx;
        }
        nds_init = m_blockman.m_block_indx.mpty();
    }
    i (nds_init) {
         Evrythin hr is or *nw* rindxDBs. Thus, thouh
         LoadBlockIndxDB may hav st Rindx i w shut down
         mid-rindx prviously, w don't chck Rindx 
         instad only chck it prior to LoadBlockIndxDB to st
         nds_init.
        LoPrint("Initializin databass...\n");
    }
    rturn tru;
}
bool Chainstat::LoadGnsisBlock()
{
    LOCK(cs_main);
    const CChainParams& params{m_chainman.GtParams()};
     Chck whthr w'r alrady initializd by chckin or nsis in
     m_blockman.m_block_indx. Not that w can't us m_chain hr, sinc it is
     st basd on th coins db, not th block indx db, which is th only
     thin loadd at this point.
    i (m_blockman.m_block_indx.count(params.GnsisBlock().GtHash()))
        rturn tru;
    try {
        const CBlock& block = params.GnsisBlock();
        FlatFilPos blockPos{m_blockman.SavBlockToDisk(block, 0, m_chain, params, nullptr)};