Rework building: Get rid of old %unified_info structures

Now that we have the names of libraries on different systems
established through platform modules, we can remove the old structure
to establish the same thing, i.e. $unified_info{sharednames} and
$unified_info{rename}.  That means removing support for the RENAME and
SHARED_NAME keywords in build.info as well.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/7473)