eth, eth/downloader, eth/fetcher: delete eth/61 code

The eth/61 protocol was disabled in #2776, this commit removes its
message handlers and hash-chain sync logic.

eth/protocol.go

@@ -28,7 +28,6 @@ import (
 
 // Constants to match up protocol versions and messages
 const (
-	eth61 = 61
 	eth62 = 62
 	eth63 = 63
 )
@@ -49,26 +48,15 @@ const (
 
 // eth protocol message codes
 const (
-	// Protocol messages belonging to eth/61
-	StatusMsg                   = 0x00
-	NewBlockHashesMsg           = 0x01
-	TxMsg                       = 0x02
-	GetBlockHashesMsg           = 0x03
-	BlockHashesMsg              = 0x04
-	GetBlocksMsg                = 0x05
-	BlocksMsg                   = 0x06
-	NewBlockMsg                 = 0x07
-	GetBlockHashesFromNumberMsg = 0x08
-
-	// Protocol messages belonging to eth/62 (new protocol from scratch)
-	// StatusMsg          = 0x00 (uncomment after eth/61 deprecation)
-	// NewBlockHashesMsg  = 0x01 (uncomment after eth/61 deprecation)
-	// TxMsg              = 0x02 (uncomment after eth/61 deprecation)
+	// Protocol messages belonging to eth/62
+	StatusMsg          = 0x00
+	NewBlockHashesMsg  = 0x01
+	TxMsg              = 0x02
 	GetBlockHeadersMsg = 0x03
 	BlockHeadersMsg    = 0x04
 	GetBlockBodiesMsg  = 0x05
 	BlockBodiesMsg     = 0x06
-	// 	NewBlockMsg       = 0x07 (uncomment after eth/61 deprecation)
+	NewBlockMsg        = 0x07
 
 	// Protocol messages belonging to eth/63
 	GetNodeDataMsg = 0x0d
@@ -117,12 +105,6 @@ type txPool interface {
 	GetTransactions() types.Transactions
 }
 
-type chainManager interface {
-	GetBlockHashesFromHash(hash common.Hash, amount uint64) (hashes []common.Hash)
-	GetBlock(hash common.Hash) (block *types.Block)
-	Status() (td *big.Int, currentBlock common.Hash, genesisBlock common.Hash)
-}
-
 // statusData is the network packet for the status message.
 type statusData struct {
 	ProtocolVersion uint32
@@ -138,19 +120,6 @@ type newBlockHashesData []struct {
 	Number uint64      // Number of one particular block being announced
 }
 
-// getBlockHashesData is the network packet for the hash based hash retrieval.
-type getBlockHashesData struct {
-	Hash   common.Hash
-	Amount uint64
-}
-
-// getBlockHashesFromNumberData is the network packet for the number based hash
-// retrieval.
-type getBlockHashesFromNumberData struct {
-	Number uint64
-	Amount uint64
-}
-
 // getBlockHeadersData represents a block header query.
 type getBlockHeadersData struct {
 	Origin  hashOrNumber // Block from which to retrieve headers
@@ -209,8 +178,3 @@ type blockBody struct {
 
 // blockBodiesData is the network packet for block content distribution.
 type blockBodiesData []*blockBody
-
-// nodeDataData is the network response packet for a node data retrieval.
-type nodeDataData []struct {
-	Value []byte
-}