core/state: remove lock (#18065)

The lock in StateDB is useless. It's only held in Copy, but Copy is safe
for concurrent use because all it does is read.

core/state/statedb.go

@@ -22,7 +22,6 @@ import (
 	"fmt"
 	"math/big"
 	"sort"
-	"sync"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
@@ -87,8 +86,6 @@ type StateDB struct {
 	journal        *journal
 	validRevisions []revision
 	nextRevisionId int
-
-	lock sync.Mutex
 }
 
 // Create a new state from a given trie.
@@ -496,9 +493,6 @@ func (db *StateDB) ForEachStorage(addr common.Address, cb func(key, value common
 // Copy creates a deep, independent copy of the state.
 // Snapshots of the copied state cannot be applied to the copy.
 func (self *StateDB) Copy() *StateDB {
-	self.lock.Lock()
-	defer self.lock.Unlock()
-
 	// Copy all the basic fields, initialize the memory ones
 	state := &StateDB{
 		db:                self.db,