Remove legacy flag for time feedback

This change removes the server flag for `time_help_and_feedback_feature_supported` as public ramps are generally discouraged in Android now. See go/android-legacy-flags. The trunk stable flag still exists, so this feature is still flagged properly.

This change also include minor refactor to simplify logic around flags now that the server flag is no longer needed.


Flag: EXEMPT removing time_help_and_feedback_feature_supported
Bug: 283239837
Change-Id: Ic5058a81186d63df4a2e57eaab4d1c120d0806bc