Remove legacy Direct Message privacy UI

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.

components/profile-modal.html

@@ -1088,36 +1088,6 @@
               role="tabpanel"
               aria-labelledby="profileNavMessages"
             >
-              <div class="card flex flex-col gap-4 p-4">
-                <div class="space-y-1">
-                  <h3 class="text-sm font-semibold text-text">Direct message privacy</h3>
-                  <p class="text-xs text-muted">
-                    Control read receipts and typing indicators for direct messages.
-                  </p>
-                </div>
-                <div class="flex flex-col gap-3">
-                  <label class="flex items-center justify-between gap-3 text-sm text-text">
-                    <span>Read receipts</span>
-                    <input
-                      id="profileMessagesReadReceiptsToggle"
-                      type="checkbox"
-                      class="switch"
-                      role="switch"
-                      aria-label="Enable read receipts"
-                    />
-                  </label>
-                  <label class="flex items-center justify-between gap-3 text-sm text-text">
-                    <span>Typing indicators</span>
-                    <input
-                      id="profileMessagesTypingToggle"
-                      type="checkbox"
-                      class="switch"
-                      role="switch"
-                      aria-label="Enable typing indicators"
-                    />
-                  </label>
-                </div>
-              </div>
               <div id="dmAppShellMount"></div>
             </section>
             <section