Changing import of crypto/sha3

- Import crypto/sha3 from `golang.org/x` instead of
`github.com/ethereum/go-ethereum`. This change was introduced in
Byzantium v1.8.21 PR: ethereum/go-ethereum#18390
For our upgrade we also need to point to golang.org/x/crypto/sha3 so the
dependencies won't break.

pkg/chain/local/local.go

@@ -9,7 +9,6 @@ import (
 	"sort"
 	"sync"
 
-	"github.com/ethereum/go-ethereum/crypto/sha3"
 	relaychain "github.com/keep-network/keep-core/pkg/beacon/relay/chain"
 	relayconfig "github.com/keep-network/keep-core/pkg/beacon/relay/config"
 	"github.com/keep-network/keep-core/pkg/beacon/relay/event"
@@ -18,6 +17,7 @@ import (
 	"github.com/keep-network/keep-core/pkg/gen/async"
 	"github.com/keep-network/keep-core/pkg/operator"
 	"github.com/keep-network/keep-core/pkg/subscription"
+	"golang.org/x/crypto/sha3"
 )
 
 var seedGroupPublicKey = []byte("seed to group public key")