login: correct comment in session_device_free()

We're not removing the pushed fd "again"; this is the only place
logind removes it from PID1.  (And stopping the fd doesn't always
cause PID1 to remove the fd itself; it depends on the device type).

src/login/logind-session-device.c

@@ -419,7 +419,7 @@ void session_device_free(SessionDevice *sd) {
         if (sd->pushed_fd) {
                 const char *m;
 
-                /* Remove the pushed fd again, just in case. */
+                /* Make sure to remove the pushed fd. */
 
                 m = strjoina("FDSTOREREMOVE=1\n"
                              "FDNAME=session-", sd->session->id);