Remove target Q check for transient night mode in UiModeManager

The target SDK check I originally added was broken since it used
the wrong UID vs User ID type.

While diagnosing, a separate concern came up about how to handle
different apps' expectations for how night mode should
work.

Checking target is weird because the system/other apps could
also be enabling car mode, and it's unclear which target level
would take precedence if multiple apps requested car mode be
enabled.

Rather than resolving that, this makes night mode transient in Q,
regardless of target version. The use cases in the wild are
probably small, and because ag/5074744 locked night mode by
default, most apps won't be affected by this behavior.

Bug: 117346726

Test: atest UiModeManagerTest
Test: manual car/night mode test app

Change-Id: If43c2f54b93e04918eeed00d8d50536bfb083630