Adopt expedited CEP-9 deprecation policy

[kenodegard]

Summary

While we have the deprecation helpers available we haven't formalized when and how deprecations occur in conda-build. This has resulted in deprecations being marked for eventual removal in the fictitious 4.0.0 release.

Tasks

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1. Switch from SemVer to CalVer (i.e., adopt CEP-8) #4975
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   epic source::anaconda type::task +3
2. Adopt 2 releases deprecation schedule (i.e., the next release marks code as deprecations (not pending deprecation), the subsequent release removes the code) Officially adopt CEP-8 and an expedited CEP-9 #5080
3. Convert ongoing deprecations to conform with expedited release schedule Officially adopt CEP-8 and an expedited CEP-9 #5080