Remove curve448 architecture specific files

Remove all architecture specific files except for the reference arch_32
version. These files provide archicture specific performance optimisation.
However they have not been integrated yet. In order to avoid review issues
they are removed for now. They may be reintroduced at a later time.

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/5105)