@Anonymous After you publish code from Visual Studio, Azure portal will set functions to be Read Only to prevent us editing pre-compiled assets in portal.
To delete any of your function in function app the suggestion is to remove the unwanted functions from your code and enable the "Remove additional files at destination" option in profile settings and redeploy your code.
But if you don't want to have any triggers then you can update the WEBSITE_RUN_FROM_PACKAGE to 0 and try deleting the function. I have tested the same at my end and couldn't observe any error. The issue could occur if you have done some changes from Kudo that would cause this behaviour. Can you navigate to Activity logs of your function app to know the cause of the failure.