Remove unused imports

src/app/services/http/user.service.ts

 import { Injectable } from '@angular/core';
-import { User } from '../../models/user';
 import { Observable } from 'rxjs/Observable';
-import { of } from 'rxjs/observable/of';
 import { HttpClient, HttpHeaders } from '@angular/common/http';
-import { ClientAuthentication } from '../../models/client-authentication';
 import { BaseHttpService } from './base-http.service';
 
 const httpOptions = {