consensus/clique, core: API cleanup (#23100)

This removes some code:

- The clique engine calculated the snapshot twice when verifying headers/blocks.

- The method GetBlockHashesFromHash in Header/Block/Lightchain was only used by tests. It
  is now removed from the API.
  
- The method GetTdByHash internally looked up the number before calling GetTd(hash, num).
  In many cases, callers already had the number, and used this method just because it has a
  shorter name. I have removed the method to make the API surface smaller.

eth/api_backend.go

@@ -194,7 +194,10 @@ func (b *EthAPIBackend) GetLogs(ctx context.Context, hash common.Hash) ([][]*typ
 }
 
 func (b *EthAPIBackend) GetTd(ctx context.Context, hash common.Hash) *big.Int {
-	return b.eth.blockchain.GetTdByHash(hash)
+	if header := b.eth.blockchain.GetHeaderByHash(hash); header != nil {
+		return b.eth.blockchain.GetTd(hash, header.Number.Uint64())
+	}
+	return nil
 }
 
 func (b *EthAPIBackend) GetEVM(ctx context.Context, msg core.Message, state *state.StateDB, header *types.Header, vmConfig *vm.Config) (*vm.EVM, func() error, error) {

eth/protocols/eth/handler_test.go

@@ -126,6 +126,12 @@ func testGetBlockHeaders(t *testing.T, protocol uint) {
 	for i := range unknown {
 		unknown[i] = byte(i)
 	}
+	getHashes := func(from, limit uint64) (hashes []common.Hash) {
+		for i := uint64(0); i < limit; i++ {
+			hashes = append(hashes, backend.chain.GetCanonicalHash(from-1-i))
+		}
+		return hashes
+	}
 	// Create a batch of tests for various scenarios
 	limit := uint64(maxHeadersServe)
 	tests := []struct {
@@ -183,7 +189,7 @@ func testGetBlockHeaders(t *testing.T, protocol uint) {
 		// Ensure protocol limits are honored
 		{
 			&GetBlockHeadersPacket{Origin: HashOrNumber{Number: backend.chain.CurrentBlock().NumberU64() - 1}, Amount: limit + 10, Reverse: true},
-			backend.chain.GetBlockHashesFromHash(backend.chain.CurrentBlock().Hash(), limit),
+			getHashes(backend.chain.CurrentBlock().NumberU64(), limit),
 		},
 		// Check that requesting more than available is handled gracefully
 		{

eth/sync.go

@@ -182,7 +182,7 @@ func (cs *chainSyncer) modeAndLocalHead() (downloader.SyncMode, *big.Int) {
 	// If we're in fast sync mode, return that directly
 	if atomic.LoadUint32(&cs.handler.fastSync) == 1 {
 		block := cs.handler.chain.CurrentFastBlock()
-		td := cs.handler.chain.GetTdByHash(block.Hash())
+		td := cs.handler.chain.GetTd(block.Hash(), block.NumberU64())
 		return downloader.FastSync, td
 	}
 	// We are probably in full sync, but we might have rewound to before the
@@ -190,7 +190,7 @@ func (cs *chainSyncer) modeAndLocalHead() (downloader.SyncMode, *big.Int) {
 	if pivot := rawdb.ReadLastPivotNumber(cs.handler.database); pivot != nil {
 		if head := cs.handler.chain.CurrentBlock(); head.NumberU64() < *pivot {
 			block := cs.handler.chain.CurrentFastBlock()
-			td := cs.handler.chain.GetTdByHash(block.Hash())
+			td := cs.handler.chain.GetTd(block.Hash(), block.NumberU64())
 			return downloader.FastSync, td
 		}
 	}