refactor: Remove unused notification code (#22833)

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## **Description**

Removes `useRegisterPushNotificationsEffect` and related unused code,
including:
- `hasInitialNotification` from
`app/util/notifications/methods/common.ts`
- `getInitialNotification` and `onBackgroundEvent` from
`app/util/notifications/services/NotificationService.ts`
- `useRegisterPushNotificationsEffect.ts` and its test file
- The usage of `useRegisterPushNotificationsEffect` in
`useNotificationHandler`

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## **Related issues**

Fixes: https://consensyssoftware.atlassian.net/browse/ASSETS-1552

## **Manual testing steps**

```gherkin
Feature: my feature name

  Scenario: user [verb for user action]
    Given [describe expected initial app state]

    When user [verb for user action]
    Then [describe expected outcome]
```

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### **After**

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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Removes useRegisterPushNotificationsEffect and initial/background
notification handlers/utilities, updating hooks, tests, and
NotificationService accordingly.
> 
> - **Notifications hooks**:
>   - Remove `useRegisterPushNotificationsEffect` and its test file.
> - Stop invoking it in `hooks/index.ts`; only call
`useStartupNotificationsEffect`.
> - Update `hooks/index.test.tsx` to assert only
`useStartupNotificationsEffect` is invoked.
> - **NotificationService (`services/NotificationService.ts`)**:
> - Remove `getInitialNotification` and `onBackgroundEvent` wrappers and
related imports/types.
> - Keep `onForegroundEvent`, badge count helpers, and display flow
intact.
> - **Methods (`methods/common.ts`)**:
>   - Remove `notifee` import and `hasInitialNotification` helper.
>   - Retain `withTimeout` and other utilities unchanged.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
7b1c858. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: Prithpal-Sooriya

app/util/notifications/hooks/index.test.tsx

@@ -2,8 +2,6 @@ import { NavigationContainerRef } from '@react-navigation/native';
 import { renderHook } from '@testing-library/react-hooks';
 import useNotificationHandler from './index';
 // eslint-disable-next-line import/no-namespace
-import * as UseRegisterPushNotificationsEffect from './useRegisterPushNotificationsEffect';
-// eslint-disable-next-line import/no-namespace
 import * as UseNotifications from './useStartupNotificationsEffect';
 
 describe('useNotificationHandler', () => {
@@ -17,20 +15,12 @@ describe('useNotificationHandler', () => {
       navigate: mockNavigate,
     } as unknown as NavigationContainerRef;
 
-    const mockUseRegisterPushNotificationsEffect = jest
-      .spyOn(
-        UseRegisterPushNotificationsEffect,
-        'useRegisterPushNotificationsEffect',
-      )
-      .mockImplementation(jest.fn());
-
     const mockUseListNotificationsEffect = jest
       .spyOn(UseNotifications, 'useStartupNotificationsEffect')
       .mockImplementation(jest.fn());
 
     return {
       mockNavigation,
-      mockUseRegisterPushNotificationsEffect,
       mockUseListNotificationsEffect,
     };
   };
@@ -39,7 +29,6 @@ describe('useNotificationHandler', () => {
     const mocks = arrangeMocks();
     renderHook(() => useNotificationHandler());
 
-    expect(mocks.mockUseRegisterPushNotificationsEffect).toHaveBeenCalled();
     expect(mocks.mockUseListNotificationsEffect).toHaveBeenCalled();
   });
 });

app/util/notifications/hooks/index.ts

@@ -1,11 +1,9 @@
-import { useRegisterPushNotificationsEffect } from './useRegisterPushNotificationsEffect';
 import { useStartupNotificationsEffect } from './useStartupNotificationsEffect';
 
 /**
- * Registers Push Notifications and lists notifications on startup.
+ * Lists notifications on startup.
  */
 const useNotificationHandler = () => {
-  useRegisterPushNotificationsEffect();
   useStartupNotificationsEffect();
 };