Cleanup: remove unneeded check (time-based) for version 4 header

thus remove !CheckBlockHeader and directly use (fCheckPOW &&
!CheckProofOfWork)

Github-Pull: #2067
Rebased-From: a4ef257

src/validation.cpp

@@ -2617,26 +2617,6 @@ bool FindUndoPos(CValidationState& state, int nFile, CDiskBlockPos& pos, unsigne
     return true;
 }
 
-bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, bool fCheckPOW)
-{
-    // Check proof of work matches claimed amount
-    if (fCheckPOW && !CheckProofOfWork(block.GetHash(), block.nBits))
-        return state.DoS(50, false, REJECT_INVALID, "high-hash", false, "proof of work failed");
-
-    if (Params().IsRegTestNet()) return true;
-
-    // Version 4 header must be used after consensus.ZC_TimeStart. And never before.
-    if (block.GetBlockTime() > Params().GetConsensus().ZC_TimeStart) {
-        if(block.nVersion < 4)
-            return state.DoS(50,false, REJECT_INVALID, "block-version", "must be above 4 after ZC_TimeStart");
-    } else {
-        if (block.nVersion >= 4)
-            return state.DoS(50,false, REJECT_INVALID, "block-version", "must be below 4 before ZC_TimeStart");
-    }
-
-    return true;
-}
-
 bool CheckColdStakeFreeOutput(const CTransaction& tx, const int nHeight)
 {
     if (!tx.HasP2CSOutputs())
@@ -2703,8 +2683,8 @@ bool CheckBlock(const CBlock& block, CValidationState& state, bool fCheckPOW, bo
 
     // Check that the header is valid (particularly PoW).  This is mostly
     // redundant with the call in AcceptBlockHeader.
-    if (!CheckBlockHeader(block, state, !IsPoS && fCheckPOW))
-        return false;
+    if (!IsPoS && fCheckPOW && !CheckProofOfWork(block.GetHash(), block.nBits))
+        return state.DoS(50, false, REJECT_INVALID, "high-hash", false, "proof of work failed");
 
     // All potential-corruption validation must be done before we do any
     // transaction validation, as otherwise we may mark the header as invalid
@@ -3070,10 +3050,6 @@ bool AcceptBlockHeader(const CBlock& block, CValidationState& state, CBlockIndex
         return true;
     }
 
-    if (!CheckBlockHeader(block, state, false)) {
-        return error("%s: CheckBlockHeader failed for block %s: %s", __func__, hash.ToString(), FormatStateMessage(state));
-    }
-
     // Get prev block index
     if (pindexPrev == nullptr && !GetPrevIndex(block, &pindexPrev, state)) {
         return false;

src/validation.h

@@ -323,7 +323,6 @@ bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex);
 bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pindex, CCoinsViewCache& coins, bool fJustCheck, bool fAlreadyChecked = false);
 
 /** Context-independent validity checks */
-bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, bool fCheckPOW = true);
 bool CheckBlock(const CBlock& block, CValidationState& state, bool fCheckPOW = true, bool fCheckMerkleRoot = true, bool fCheckSig = true);
 bool CheckWork(const CBlock block, CBlockIndex* const pindexPrev);