enhance(backend): use native fetch instead of node-fetch polyfill

packages/backend/test/e2e/endpoints.ts

@@ -6,9 +6,6 @@
 process.env.NODE_ENV = 'test';
 
 import * as assert from 'assert';
-// node-fetch only supports it's own Blob yet
-// https://github.com/node-fetch/node-fetch/pull/1664
-import { Blob } from 'node-fetch';
 import { api, castAsError, initTestDb, post, signup, simpleGet, uploadFile } from '../utils.js';
 import type * as misskey from 'misskey-js';
 import { MiUser } from '@/models/_.js';

packages/backend/test/unit/CaptchaService.ts

@@ -5,7 +5,6 @@
 
 import { afterAll, beforeAll, beforeEach, describe, expect, jest } from '@jest/globals';
 import { Test, TestingModule } from '@nestjs/testing';
-import { Response } from 'node-fetch';
 import {
 	CaptchaError,
 	CaptchaErrorCode,

packages/backend/test/utils.ts

@@ -9,10 +9,8 @@ import { basename, isAbsolute } from 'node:path';
 import { randomUUID } from 'node:crypto';
 import { inspect } from 'node:util';
 import WebSocket, { ClientOptions } from 'ws';
-import fetch, { File, RequestInit, type Headers } from 'node-fetch';
 import * as htmlParser from 'node-html-parser';
 import { DataSource } from 'typeorm';
-import { type Response } from 'node-fetch';
 import Fastify from 'fastify';
 import { entities } from '../src/postgres.js';
 import { loadConfig } from '../src/config.js';