Removes the "Direct message privacy" section from the profile modal's Messages tab, as these settings are now managed via the AppShell (gear icon).
- Removed privacy section HTML from `components/profile-modal.html`.
- Updated `js/ui/profileModalController.js` to remove legacy DOM references and event listeners.
- Preserved `handleReadReceiptsToggle` and `handleTypingIndicatorsToggle` methods for AppShell integration.
- Updated `syncDmPrivacySettingsUi` to be a no-op to prevent errors in existing call sites.
