move-mostly: Make fHavePruned a BlockMan member

[META] In the next commit, we move the clearing of fHavePruned to
       BlockManager::Unload()

src/node/chainstate.cpp

@@ -65,7 +65,7 @@ std::optional<ChainstateLoadingError> LoadChainstate(bool fReset,
 
     // Check for changed -prune state.  What we are concerned about is a user who has pruned blocks
     // in the past, but is now trying to run unpruned.
-    if (fHavePruned && !fPruneMode) {
+    if (chainman.m_blockman.fHavePruned && !fPruneMode) {
         return ChainstateLoadingError::ERROR_PRUNED_NEEDS_REINDEX;
     }