I’m developing functions in Visual Studio instead of developing them in the Azure Portal. If you open the function in the Azure Portal you will receive the following message:
Your app is currently in read-only mode because you have published a generated function.json. Changes made to function.json will not be honored by the Functions runtime.
One of the consequences of this message is, that it seems like you can’t remove the function anymore. Very annoying, but … there’s a workaround. When you open the function container under menu option Function Apps, you will see two tabs at the top: Overview and Platform Settings. Go to Platform Settings and select the App Service Editor. You will see all functions displayed. Right-click the function you want to delete and select Delete.
Apparently a simple fix of this issue will go out soon.