Set navBarDarkIntensity based on dark theme in SUW

- Also remove old tinting based on textColorPrimary, as it's no longer necessary with dark intensity tinting.

Test: Run SetupWizardTestActivity in both dark and light theme, ensure back button visible
Fixes: 204384193
Change-Id: I2dc2e94bc0318ded62419b9ae0eed719db289d7f
1 file changed