Remove unused `missed_update` state (#25832)

app/javascript/mastodon/reducers/index.ts

@@ -26,7 +26,6 @@ import lists from './lists';
 import markers from './markers';
 import media_attachments from './media_attachments';
 import meta from './meta';
-import { missedUpdatesReducer } from './missed_updates';
 import { modalReducer } from './modal';
 import mutes from './mutes';
 import notifications from './notifications';
@@ -82,7 +81,6 @@ const reducers = {
   suggestions,
   polls,
   trends,
-  missed_updates: missedUpdatesReducer,
   markers,
   picture_in_picture,
   history,

app/javascript/mastodon/reducers/missed_updates.ts

-import { Record } from 'immutable';
-
-import type { Action } from 'redux';
-
-import { focusApp, unfocusApp } from '../actions/app';
-import { NOTIFICATIONS_UPDATE } from '../actions/notifications';
-
-interface MissedUpdatesState {
-  focused: boolean;
-  unread: number;
-}
-const initialState = Record<MissedUpdatesState>({
-  focused: true,
-  unread: 0,
-})();
-
-export function missedUpdatesReducer(
-  state = initialState,
-  action: Action<string>
-) {
-  switch (action.type) {
-    case focusApp.type:
-      return state.set('focused', true).set('unread', 0);
-    case unfocusApp.type:
-      return state.set('focused', false);
-    case NOTIFICATIONS_UPDATE:
-      return state.get('focused')
-        ? state
-        : state.update('unread', (x) => x + 1);
-    default:
-      return state;
-  }
-}