On VMS, massage the fetch file names to remove the generation number

The generation number is ';nnn' at the end of the file name fetched
with readdir().  Because rehash checks for specific extensions and
doesn't expect an additional generation number, the easiest is to
massage the received file name early by simply removing the generation
number.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2717)