how to remove NbAuthService

### Issue type

**I'm submitting a ...** (check one with "x")

* [ ] bug report
* [ ] feature request

### Issue description

**Current behavior:**

**Expected behavior:**

**Steps to reproduce:**

**Related code:**

```
/*
* Copyright (c) Akveo 2019. All Rights Reserved.
* Licensed under the Single Application / Multi Application License.
* See LICENSE_SINGLE_APP / LICENSE_MULTI_APP in the 'docs' folder for license information on type of purchased license.
*/
import { BrowserModule } from '@angular/platform-browser';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { NgModule, Injector, APP_INITIALIZER } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';
import { CoreModule } from './@core/core.module';
import { RouterModule } from '@angular/router';
import { AppComponent } from './app.component';
import { AppRoutingModule } from './app-routing.module';
import { ThemeModule } from './@theme/theme.module';
//import { AuthModule } from './@auth/auth.module';
import { InitUserService } from './@theme/services/init-user.service';
//import { NbSecurityModule, NbRoleProvider } from '@nebular/security';
import {
NbChatModule,
NbDatepickerModule,
NbDialogModule,
NbMenuModule,
NbSidebarModule,
NbToastrModule,
NbWindowModule,
NbCalendarModule,
NbSelectModule,
} from '@nebular/theme';

export function init_app(injector: Injector) {
return () =>
new Promise((resolve: Function) => {
const initUserService = injector.get(InitUserService);
initUserService.initCurrentUser().subscribe(() => { },
() => resolve(), () => resolve());
});
}

@NgModule({
declarations: [
AppComponent,
],
imports: [
RouterModule,
BrowserModule,
BrowserAnimationsModule,
HttpClientModule,
AppRoutingModule,
NbSelectModule,

ThemeModule.forRoot(),
//AuthModule.forRoot(),

NbSidebarModule.forRoot(),
NbMenuModule.forRoot(),
NbDatepickerModule.forRoot(),
NbDialogModule.forRoot(),
NbWindowModule.forRoot(),
NbToastrModule.forRoot(),
NbChatModule.forRoot({
messageGoogleMapKey: 'AIzaSyA_wNuCzia92MAmdLRzmqitRGvCF7wCZPY',
}),
CoreModule.forRoot(),

//NbSecurityModule.forRoot(),
],
bootstrap: [AppComponent],
providers: [],
})
export class AppModule {
}

```

### Other information:
I want to remove the nebular authentication module, since I want to use Auth0, trying to remove it gives me several errors
```
ERROR NullInjectorError: StaticInjectorError(AppModule)[AppComponent -> NbAuthService]:
StaticInjectorError(Platform: core)[AppComponent -> NbAuthService]:
NullInjectorError: No provider for NbAuthService!
```