Remove the `ServiceBusEntity` enumeration

[stijnmoreels]

Is your feature request related to a problem? Please describe.
When creating Azure Service Bus message pumps, we had to determine for which entity type the message pump was created. We added a ServiceBusEntity enumeration to make this distinction. Later, we chose to use the built-in ServiceBusEntityType enumeration, making this one obsolete.

Describe the solution you'd like
Remove the ServiceBusEntity enumeration.