Switch future deprecation version from 1.2.0 to 3.0

This is in preparation for a switch to MAJOR.MINOR.PATCH versioning
and calling the next major version 3.0.0.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)