These changes remove all of the preexisting version checking for
individual features, wiping the slate clean with an overall minimum
requirement of a future TFP-API-Version 2.5, which at the time of this
writing is expected to be TFE v202112-1.

It also actually provides that expected TFE version as an actionable
error message, rather than generically saying that it isn't supported or
using the somewhat opaque API version header.