Various code inspection resolutions (#7438)

* remove unused code

* remove defer use in loop

* Remove unused methods and constants

* gofmt and gaz

* nilness check

* remove unused args

* Add TODO for refactoring subscribeWithBase to remove unused arg. It seems too involved to include in this sweeping PR. https://github.com/prysmaticlabs/prysm/issues/7437

* replace empty slice declaration

* Remove unnecessary type conversions

* remove redundant type declaration

* rename receivers to be consistent

* Remove bootnode query tool. It is now obsolete by discv5

* Remove relay node. It is no longer used or supported

* Revert "Remove relay node. It is no longer used or supported"

This reverts commit 4bd7717334.

* Delete unused test directory

* Delete unsupported gcp startup script

* Delete old k8s script

* build fixes

* fix build

* go mod tidy

* revert slasher/db/kv/block_header.go

* fix build

* remove redundant nil check

* combine func args

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>
Co-authored-by: Victor Farazdagi <simple.square@gmail.com>

tools/bootnode/bootnode_test.go

@@ -9,7 +9,6 @@ import (
 	"testing"
 	"time"
 
-	"github.com/btcsuite/btcd/btcec"
 	"github.com/ethereum/go-ethereum/p2p/discover"
 	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/libp2p/go-libp2p-core/crypto"
@@ -69,7 +68,7 @@ func TestPrivateKey_ParsesCorrectly(t *testing.T) {
 
 	extractedKey := extractPrivateKey()
 
-	rawKey := (*ecdsa.PrivateKey)((*btcec.PrivateKey)(privKey.(*crypto.Secp256k1PrivateKey)))
+	rawKey := (*ecdsa.PrivateKey)(privKey.(*crypto.Secp256k1PrivateKey))
 
 	r, s, err := ecdsa.Sign(rand.Reader, extractedKey, []byte{'t', 'e', 's', 't'})
 	require.NoError(t, err)