fix megacheck issue: simplified return err

db.go

@@ -725,10 +725,7 @@ func (db *DB) Delete(mint, maxt int64, ms ...labels.Matcher) error {
 	g.Go(func() error {
 		return db.head.Delete(mint, maxt, ms...)
 	})
-	if err := g.Wait(); err != nil {
-		return err
-	}
-	return nil
+	return g.Wait()
 }
 
 // CleanTombstones re-writes any blocks with tombstones.