Dont create pcoinsTip until after ReplayBlocks.

This requires that we not access pcoinsTip in InitBlockIndex's
FlushStateToDisk (so we just skip it until later in AppInitMain)
and the LoadChainTip in LoadBlockIndex (which there is already one
later in AppinitMain, after ReplayBlocks, so skipping it there is
fine).

Includes some simplifications by Suhas Daftuar and Pieter Wuille.

src/validation.cpp

@@ -3420,7 +3420,6 @@ bool static LoadBlockIndexDB(const CChainParams& chainparams)
     pblocktree->ReadFlag("txindex", fTxIndex);
     LogPrintf("%s: transaction index %s\n", __func__, fTxIndex ? "enabled" : "disabled");
 
-    LoadChainTip(chainparams);
     return true;
 }
 
@@ -3783,8 +3782,6 @@ bool InitBlockIndex(const CChainParams& chainparams)
             CBlockIndex *pindex = AddToBlockIndex(block);
             if (!ReceivedBlockTransactions(block, state, pindex, blockPos, chainparams.GetConsensus()))
                 return error("LoadBlockIndex(): genesis block not accepted");
-            // Force a chainstate write so that when we VerifyDB in a moment, it doesn't check stale data
-            return FlushStateToDisk(chainparams, state, FLUSH_STATE_ALWAYS);
         } catch (const std::runtime_error& e) {
             return error("LoadBlockIndex(): failed to initialize block database: %s", e.what());
         }