Websites: Update help for Remove-AzureRmWebAppSlot, example doesn't have the slot in the command

### Description

https://docs.microsoft.com/en-us/powershell/module/azurerm.websites/remove-azurermwebappslot?view=azurermps-5.4.0 - see comments missing slot in the command

### Script/Steps for Reproduction



```powershell

```

### Module Version

4.1.0      AzureRM.Websites 
```