Unxfail test_settings_cell_data.py as it is now stable

This test has been stable for some time [1].

```v1.0.1``` -> merge
```v1-train``` -> ignore
```master``` -> ignore

[1] http://qa-selenium.mv.mozilla.com:8080/view/B2G%20Inari/job/b2g.inari.gaia.v1.0.1.ui.xfail.ril/230/testReport/%28root%29/TestSettingsCellData/history/?