Simplify and clarify VMS specifics in File::Copy.

Simplify and clarify VMS specifics in File::Copy.

4c38808d92b95 added some logic to make a "to" path with no
directory component inherit from the current working directory
rather than the directory portion of the "from" path.  It also
added a trailing dot to make null file types unambiguous.  But
the comments emphasized the latter and made no mentin of the
former, and the implementation was unnecessarily complex.