Remove paramcoq from platform

1.1.3+rocq9.0 will be the last release. It is no longer maintained other than as a test for Rocq OCaml API. It's only dependency in the platform, CoqEAL, is ported to coq-elpi derive (already in the platform) starting with Rocq 9.
No opinion on whether paramcoq should be included in the next 9.0 platform but it will then have to be removed.