[SciPy-Dev] Deprecate hyp2f0, hyp1f2, and hyp3f0

[Joshua Wilson]

Hello everyone,

I would like to draw your attention to

https://github.com/scipy/scipy/issues/8443

which proposes deprecating the hypergeometric functions hyp2f0,
hyp1f2, and hyp3f0. It appears that they were intended to be internal
helper functions for Cephes and got included in the SciPy API by
accident (see issue for more details).

Note that I am *not* proposing we deprecate the important
hypergeometric functions, namely `hyp0f1` (confluent hypergeometric
limit function), `hyp1f1`, `hyperu` (confluent hypergeometric
functions), and `hyp2f1` (Gaussian hypergeometric function).

- Josh