chore: fix license of of Mozilla data (#1335)

They switched to Creatice Commons Zero in 2018 https://github.com/mdn/data/blob/main/LICENSE

I cannot find that the CSSData template mentioned in the original README
is used anywhere in the code right now and the template does not exist
on MDN any more either.

packages/postcss-reduce-initial/README.md

@@ -85,10 +85,7 @@ See [CONTRIBUTORS.md](https://github.com/cssnano/cssnano/blob/master/CONTRIBUTOR
 
 ## License
 
-[Template:CSSData] by Mozilla Contributors is licensed under [CC-BY-SA 2.5].
-
-[template:cssdata]: https://developer.mozilla.org/en-US/docs/Template:CSSData
-[cc-by-sa 2.5]: http://creativecommons.org/licenses/by-sa/2.5/
+This program uses a list of CSS properties derived from data maintained my the MDN team at Mozilla and licensed under the [CC0 1.0 Universal Public Domain Dedication](https://creativecommons.org/publicdomain/zero/1.0/).
 
 MIT © [Ben Briggs](http://beneb.info)