openssl rehash: no more need to massage the files on VMS

OPENSSL_DIR_read() now returns unique file names on VMS, no generation
number.  We therefore do not need to handle that case in apps/rehash.c
any more.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5602)