Ignore ORDINALS in build.info files, and remove its documentation

Following the changes that removed Makefile.shared, we also changed
the generation of .def / .map / .opt files from ordinals more
explicit, removing the need to the "magic" ORDINALS declaration.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4993)