Removal of legacy precompiled model

[fabiocav]

Discussion for proposal #1974

[brettsam]

Questions during meeting:

• What are the historical reasons for keeping this around? Are there major products relying on this behavior?
• Removing this could lose some "dynamic" host.json configuration scenarios -- for example, manually modifying values in host.json does not work for the attribute-based model.
• Sample of this is here -- https://github.com/Azure/azure-functions-host/wiki/Precompiled-functions
• Need investigation of subs currently using this support today.
• Would removing this result in us removing a "known" amount of support for some "unknown" amount of support with a new model. Would that be valuable work for the team?
• Can we add a detector for this instead?

We vote to reject this...