Remove NEW_TOKEN public api

Remove NEW_TOKEN public api

@sashan and I were discussing the usefulness of the public facing api
for NEW_TOKEN support, and he has concerns over its usefulness and our
being stuck with it if we need to make changes later.  Given that it is
a convience api for using multiple CTX-es to share a cache, its fine if
we remove it for now, as that seems like a less common use case.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26517)