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

consensus/reactor_test.go

@@ -235,7 +235,7 @@ func TestReactorCreatesBlockWhenEmptyBlocksFalse(t *testing.T) {
 
 	// send a tx
 	if err := assertMempool(css[3].txNotifier).CheckTx([]byte{1, 2, 3}, nil); err != nil {
-		//t.Fatal(err)
+		t.Error(err)
 	}
 
 	// wait till everyone makes the first new block