In revision 1.351, All files/directories in ${CHROOTDIR}/usr/ports/distfiles
are removed, because ports.tgz includes distfiles by accident.

However, removing files/directories is *not* mandatory. The only
requirement is "ports.tgz doesn't include distfiles/* but distfiles
directory itself". If this is correct, the right way is to set an
option to tar(1), not to include these files.

This commit is based on PR: 34194, but a little bit of modification
is made by me (original patch doesn't include 'distfiles' directory).

PR: 34194
Reviewed by: Adrian Steinmann <ast@marabu.ch> (PR submitter)
MFC after: 9 days