Bug 925702 - Reenable tests/functional/dialer tests on aurora

Remove xfails for all tests in tests/functional/dialer on aurora since bug 904625, bug 914823 and bug 915038 have been fixed.

In order to re-enable all the tests, this locator needs to be updated:
https://github.com/mozilla-b2g/gaia/blob/v1.2/tests/python/gaia-ui-tests/gaiatest/apps/phone/regions/call_screen.py#L16