Delete User by ID does not return an error, even if the deleted ID is set

[junyama]

Here is the way to reproduce the issue:

1. Create a new User by using Create new User API
2. Check ID of the user created at the step 1) by using Get All Users with Paging API
3. Delete the user by using Delete User by ID API with the ID
4. Delete the user by using Delete User by ID API with the same ID again

Even if you call Delete User by ID API with ID of a user which was already deleted, the return message of API is as follows:

{ "status": "OK", "code": 200, "message": "User was successfully deleted" }