add staticcheck linting (#3828)

cleanup to add linter

    grpc change:
        https://godoc.org/google.golang.org/grpc#WithContextDialer
        https://godoc.org/google.golang.org/grpc#WithDialer
        grpc/grpc-go#2627
    prometheous change:
        due to UninstrumentedHandler, being deprecated in the future
    empty branch = empty if or else statement
        didn't delete them entirely but commented
        couldn't find a reason to have them
    could not replicate the issue #3406
        but if want to keep it commented then we should comment out the if statement as well

p2p/switch_test.go

@@ -16,7 +16,7 @@ import (
 	"testing"
 	"time"
 
-	stdprometheus "github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
@@ -348,7 +348,7 @@ func TestSwitchStopsNonPersistentPeerOnError(t *testing.T) {
 }
 
 func TestSwitchStopPeerForError(t *testing.T) {
-	s := httptest.NewServer(stdprometheus.UninstrumentedHandler())
+	s := httptest.NewServer(promhttp.Handler())
 	defer s.Close()
 
 	scrapeMetrics := func() string {