daemon-util: introduce notify_remove_fd()

It is equivalent to notify_remove_fd_warn() but logs in debug level on
failure.

src/shared/daemon-util.h

@@ -21,6 +21,7 @@ static inline void notify_on_cleanup(const char **p) {
                 (void) sd_notify(false, *p);
 }
 
+int notify_remove_fd(const char *name);
 int notify_remove_fd_warn(const char *name);
 int notify_remove_fd_warnf(const char *format, ...) _printf_(1, 2);
 int close_and_notify_warn(int fd, const char *name);