[upower] clean up unused label and variables

```
csd-power-manager.c:1025:1: warning: label 'out' defined but not used [-Wunused-label]
 out:
 ^
csd-power-manager.c:1002:17: warning: unused variable 'error' [-Wunused-variable]
         GError *error = NULL;
                 ^
csd-power-manager.c:1001:18: warning: unused variable 'ret' [-Wunused-variable]
         gboolean ret;
                  ^
```