[css-contain-1] Update and trim the Previous Version list

Author: frivoal

css-contain-1/Overview.bs

@@ -8,14 +8,8 @@ Work Status: completed
 Group: csswg
 ED: https://drafts.csswg.org/css-contain-1/
 TR: https://www.w3.org/TR/css-contain-1/
+Previous Version: https://www.w3.org/TR/2020/REC-css-contain-1-20201222/
 Previous Version: https://www.w3.org/TR/2019/REC-css-contain-1-20191121/
-Previous Version: https://www.w3.org/TR/2019/PR-css-contain-1-20191015/
-Previous Version: https://www.w3.org/TR/2019/CR-css-contain-1-20190430/
-Previous Version: https://www.w3.org/TR/2018/CR-css-contain-1-20181108/
-Previous Version: https://www.w3.org/TR/2018/CR-css-contain-1-20180524/
-Previous Version: https://www.w3.org/TR/2017/CR-css-contain-1-20170808/
-Previous Version: https://www.w3.org/TR/2017/WD-css-contain-1-20170419/
-Previous Version: https://www.w3.org/TR/2017/WD-css-contain-1-20170221/
 Editor: Tab Atkins, Google, http://xanthir.com/contact/, w3cid 42199
 Editor: Florian Rivoal, On behalf of Bloomberg, https://florian.rivoal.net/, w3cid 43241
 Abstract: This CSS module describes the 'contain' property, which indicates that the element's subtree is independent of the rest of the page. This enables heavy optimizations by user agents when used well.