Fix ActiveDirectroy secenario test

## Description
Test-NewADServicePrincipalWithoutApp in ActiveDirectroy secenario test is legary now.

````
# Test
$servicePrincipal = New-AzADServicePrincipal -DisplayName $displayName
$role = Get-AzRoleAssignment -ObjectId $servicePrincipal.Id

# Assert
Assert-NotNull $servicePrincipal
Assert-AreEqual $servicePrincipal.DisplayName $displayName
Assert-Null $role
````
When role is not specified explicitly, New-AzADServicePrincipal has a default role, which is "Contributor". And so the $role is not nul in the test case.
## Cost