chore: remove dead settings code and stale imports

[dclstn]

Cleanup from an audit of 7.7.25 to master:

• Unused useRef imports left behind by the useEntryListState extraction (feat: add self bot timers #8201).
• SettingKeywords.module.css classes that moved to the shared SettingEntryTable stylesheet, and the styles.channelsColumn reference to a class that never existed. The keywords panel now uses the shared settingGroupContent and emptyText like the other tables.
• showNewBadge plumbing on SettingCheckbox and SettingPrimaryColorRadio, with no callers since qol: remove new badges from settings and retire promotions #8203.
• showComingSoonBadge on SettingWrapper, unused since timers shipped.
• Unused .vertical and .reverse classes in SettingWrapper.module.css.
• The load.chat listener in reduced_motion, which re-toggled a body class that already tracks both of its inputs.
• A stale comment in SideNavigation.module.css about the Changelog button.

No behaviour change. Lint and build pass.

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