Use system day/night to switch theme instead of from intent extra.

Use value-night to give theme instead of directly from intent extra when Setup day/nNight mode enabled and in Setup flow

Before:
<vision settings>
https://hsv.googleplex.com/4837266235064320
<wifi dialog>
https://hsv.googleplex.com/5687053981319168
<lock screen with disabling button>
https://hsv.googleplex.com/4843506419892224
<lock screen with enabling button>
https://hsv.googleplex.com/5650348922372096
<fingerprint intro>
https://hsv.googleplex.com/5133769046491136
<fingerprint touch>
https://hsv.googleplex.com/5681937198874624
<fingerprint left touch>
https://hsv.googleplex.com/5767441676238848
<squeeze release>
https://hsv.googleplex.com/6632476812247040

After:
<vision settings>
https://hsv.googleplex.com/6213298875793408
<wifi dialog>
https://hsv.googleplex.com/6025790804197376
<lock screen with disabling button>
https://hsv.googleplex.com/5747461219942400
<lock screen with enabling button>
https://hsv.googleplex.com/5766700781797376
<fingerprint intro>
https://hsv.googleplex.com/6751334529236992
<fingerprint touch>
https://hsv.googleplex.com/5625963293442048
<fingerprint left touch>
https://hsv.googleplex.com/4518139360444416
<squeeze release>
https://hsv.googleplex.com/5220720579706880

Bug: 169734655
Test: robo test
Change-Id: I4aab843e28a932c7b823f36f1d8df1e5b2341f4e