Revert "ethdb/memorydb: init map with known size (ethereum#27241)"

This reverts commit 7f60d82.

ethdb/memorydb/memorydb.go

@@ -342,7 +342,7 @@ func newSnapshot(db *Database) *snapshot {
 	db.lock.RLock()
 	defer db.lock.RUnlock()
 
-	copied := make(map[string][]byte, len(db.db))
+	copied := make(map[string][]byte)
 	for key, val := range db.db {
 		copied[key] = common.CopyBytes(val)
 	}