util: move strange Read2000Uint256Hashes() into storage

It's the only user of it.

pkg/core/storage/helpers.go

@@ -1,6 +1,7 @@
 package storage
 
 import (
+	"bytes"
 	"encoding/binary"
 	"sort"
 
@@ -55,7 +56,7 @@ func HeaderHashes(s Store) ([]util.Uint256, error) {
 	hashMap := make(map[uint32][]util.Uint256)
 	s.Seek(IXHeaderHashList.Bytes(), func(k, v []byte) {
 		storedCount := binary.LittleEndian.Uint32(k[1:])
-		hashes, err := util.Read2000Uint256Hashes(v)
+		hashes, err := read2000Uint256Hashes(v)
 		if err != nil {
 			panic(err)
 		}
@@ -78,3 +79,15 @@ func HeaderHashes(s Store) ([]util.Uint256, error) {
 
 	return hashes, nil
 }
+
+// read2000Uint256Hashes attempts to read 2000 Uint256 hashes from
+// the given byte array.
+func read2000Uint256Hashes(b []byte) ([]util.Uint256, error) {
+	r := bytes.NewReader(b)
+	lenHashes := util.ReadVarUint(r)
+	hashes := make([]util.Uint256, lenHashes)
+	if err := binary.Read(r, binary.LittleEndian, hashes); err != nil {
+		return nil, err
+	}
+	return hashes, nil
+}

pkg/util/io.go

@@ -1,7 +1,6 @@
 package util
 
 import (
-	"bytes"
 	"encoding/binary"
 	"io"
 )
@@ -89,15 +88,3 @@ func WriteVarBytes(w io.Writer, b []byte) error {
 	}
 	return binary.Write(w, binary.LittleEndian, b)
 }
-
-// Read2000Uint256Hashes attempt to read 2000 Uint256 hashes from
-// the given byte array.
-func Read2000Uint256Hashes(b []byte) ([]Uint256, error) {
-	r := bytes.NewReader(b)
-	lenHashes := ReadVarUint(r)
-	hashes := make([]Uint256, lenHashes)
-	if err := binary.Read(r, binary.LittleEndian, hashes); err != nil {
-		return nil, err
-	}
-	return hashes, nil
-}