This has been a pkglint warning for several years now, and pkglint can even
fix it automatically. And it did for this commit.
Only in lang/mercury, two passes of autofixing were necessary because there
were nested variables.
Problems found with existing distfiles:
distfiles/D6.data.ros.gz
distfiles/cstore0.2.tar.gz
distfiles/data4.tar.gz
distfiles/sphinx-2.2.7-release.tar.gz
No changes made to the cstore or mariadb55-client distinfo files.
Otherwise, existing SHA1 digests verified and found to be the same on
the machine holding the existing distfiles (morden). All existing
SHA1 digests retained for now as an audit trail.