Apply more mechanical simplifications using recent Go features

This is a follow-up on the `go fix` run in commit
0210c5fd92.

That commit recorded the automated updates.

This one applies further simplifications that are mechanical and do not
involve logic changes, but are outside of what `go fix` did.

It also removes some now-obsolete comments and statements.

internal/queue/dsn_test.go

@@ -2,7 +2,7 @@ package queue
 
 import (
 	"fmt"
-	"sort"
+	"slices"
 	"strings"
 	"testing"
 )
@@ -182,7 +182,7 @@ func printDiff(print func(s string), expected, got string) {
 
 	// sort the lines, to make it easier to see the differences (this works
 	// ok when there's few, horrible when there's lots).
-	sort.Strings(lines)
+	slices.Sort(lines)
 
 	// print diff of expected vs. got
 	seen := map[string]bool{}