Remove PJ files from non-sample projects

[guardrex]

Fixes #5496

What this does

This PR removes the project.json files from these projects:

• common\samples\WebApplication1
• migration\http-modules\sample\Asp.Net.Core
• mvc\controllers\routing\sample\main
• mvc\controllers\routing\sample\AreasRouting
• mvc\controllers\application-model\sample\src\AppModelSample

These projects aren't samples linked from their topics. They only provide code snippet content.

---

What this doesn't do

This PR doesn't remove the project.json file from these project.json/.xproj-era projects:

• fundamentals\servers\aspnet-core-module\sample
• fundamentals\dependency-injection\sample\DependencyInjectionSample
• fundamentals\error-handling\sample
• fundamentals\app-state\sample\src\WebAppSession
• data\entity-framework-6\sample\MVCCore
• fundamentals\middleware\index\sample\Middleware
• fundamentals\middleware\index\sample\Culture
• fundamentals\middleware\index\sample\Chain
• fundamentals\owin\sample\src\OwinSample
• fundamentals\owin\sample\src\NowinWebSockets
• fundamentals\owin\sample\src\NowinSample
• migration\configuration\samples\WebApp1\src\WebApp1
• migration\webapi\sample\ProductsCore
• mvc\controllers\dependency-injection\sample\src\ControllerDI
• mvc\models\file-uploads\sample\FileUploadSample
• mvc\views\dependency-injection\sample\src\ViewInjectSample
• performance\caching\memory\sample\WebCache
• performance\caching\response\sample
• mobile\native-mobile-backend\sample\ToDoApi\src\ToDoApi
• mvc\views\working-with-forms\sample\final

All of those projects are linked into their topics as samples. They should be updated as part of the effort on Sample Update Tracking Issue #5495. At the conclusion of that work and following this PR, our IDEs (e.g., VSC) should stop flagging us to upgrade projects when we open the repo locally for work.