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>

beacon-chain/core/helpers/shuffle_test.go

@@ -60,7 +60,7 @@ func TestSplitIndices_OK(t *testing.T) {
 }
 
 func TestShuffleList_Vs_ShuffleIndex(t *testing.T) {
-	list := []uint64{}
+	var list []uint64
 	listSize := uint64(1000)
 	seed := [32]byte{123, 42}
 	for i := uint64(0); i < listSize; i++ {
@@ -124,7 +124,7 @@ func BenchmarkShuffleList(b *testing.B) {
 }
 
 func TestShuffledIndex(t *testing.T) {
-	list := []uint64{}
+	var list []uint64
 	listSize := uint64(399)
 	for i := uint64(0); i < listSize; i++ {
 		list = append(list, i)