Deprecate the no-op custom_jvp_call_jaxpr_p import stub.
The `custom_jvp_call_jaxpr_p` primitive has not been used for a long time, and the existing object is just an import stub. Let's try to clean up some @mattjj TODOs!
Sadly, since this lives in the public API, I think we need to do a full deprecation cycle, so let's at least get that started!
PiperOrigin-RevId: 758415957
