refactor: remove unused imports in leaderboard handlers and services

Remove the unused import of CurrentMirageUser in the leaderboard-entries
mirage handler and LeaderboardEntryModel in the preferred-language-leaderboard
service to clean up the codebase and improve maintainability.

Author: rohitpaulk

app/services/preferred-language-leaderboard.ts

@@ -3,7 +3,6 @@ import LocalStorageService from 'codecrafters-frontend/services/local-storage';
 import { tracked } from '@glimmer/tracking';
 import { action } from '@ember/object';
 import type AuthenticatorService from './authenticator';
-import LeaderboardEntryModel from 'codecrafters-frontend/models/leaderboard-entry';
 import type Store from '@ember-data/store';
 
 class StoredData {

mirage/handlers/leaderboard-entries.js

@@ -1,5 +1,3 @@
-import CurrentMirageUser from 'codecrafters-frontend/mirage/utils/current-mirage-user';
-
 export default function (server) {
   server.get('/leaderboard-entries', function (schema, request) {
     if (!request.queryParams.leaderboard_id) {