Hide room version fragments from table of contents (#3479)

The entries were text-less and not really helping anyone. They are included as pages because we need them for templating, but we don't need people to be able to land on them directly.

content/rooms/fragments/v3-handling-redactions.md

@@ -1,6 +1,5 @@
 ---
-# unused frontmatter - just fixing a hugo issue where it doesn't parse
-# shortcodes at the start of a file.
+toc_hide: true
 ---
 
 {{% added-in this=true %}} In room versions 1 and 2, redactions were