Fix PR 4098 (#4106)

Signed-off-by: Fabio Di Fabio <fabio.difabio@consensys.net>

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/sync/backwardsync/BackwardChain.java

@@ -95,22 +95,6 @@ public class BackwardChain {
       return;
     }
     BlockHeader firstHeader = firstStoredAncestor.get();
-    if (firstHeader.getNumber() != blockHeader.getNumber() + 1) {
-      throw new BackwardSyncException(
-          "Wrong height of header "
-              + blockHeader.getHash().toHexString()
-              + " is "
-              + blockHeader.getNumber()
-              + " when we were expecting "
-              + (firstHeader.getNumber() - 1));
-    }
-    if (!firstHeader.getParentHash().equals(blockHeader.getHash())) {
-      throw new BackwardSyncException(
-          "Hash of header does not match our expectations, was "
-              + blockHeader.toLogString()
-              + " when we expected "
-              + firstHeader.getParentHash().toHexString());
-    }
     headers.put(blockHeader.getHash(), blockHeader);
     chainStorage.put(blockHeader.getHash(), firstStoredAncestor.get().getHash());
     firstStoredAncestor = Optional.of(blockHeader);