Fix lint warnings and std lib deprecations

cmd/backup/lock.go

@@ -15,10 +15,12 @@ import (
 // caller invokes the returned release func. In case the lock is currently blocked
 // by another execution, it will repeatedly retry until the lock is available
 // or the given timeout is exceeded.
+//
+//lint:ignore U1000 Keep unused function
 func (s *script) lock(lockfile string) (func() error, error) {
 	start := time.Now()
 	defer func() {
-		s.stats.LockedTime = time.Now().Sub(start)
+		s.stats.LockedTime = time.Since(start)
 	}()
 
 	retry := time.NewTicker(5 * time.Second)