VMS: stop trying to build shared libraries from static ones

The possibility to do this was killed when we started producing object
file names with encoded intention (and possibly different builds), and
leads to build errors.

With that, 'libobj2shlib' is renamed to 'obj2shlib' to reflect this
design change.  The old name is still used if the new one isn't
available, for the sake of backward compatibility.

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7198)