chore(remove): az func service-bus project

[stijnmoreels]

The Messaging repository previously supported dedicated types like Azure Functions, but due to budget and maintainence costs, this is increasingly harder to keep up-to-date.

This PR removes the Azure Functions-specific library for Azure Service bus from the project solution. This is possible in a minor version as:

• The Azure Functions project is a separate project, which means a separate NuGet package. Removing the project now does not result in a breaking change when releasing v2.1.
• The Azure Functions project mostly contains functionality to extract correlation information from binding inputs of Azure Function triggers. This was required in the past, but is now obsolete since the trigger types have now strongly-typed inputs with the correlation information available.

This is related to the exercise described in #470.

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