youtube.lua: update comments about fmt URL parameter

Link to old Wikipedia page revision where itag parameter formats were
actually still described.

share/lua/playlist/youtube.lua

@@ -758,9 +758,12 @@ function parse()
         or string.match( vlc.path, "/shorts/" )
     then -- This is the HTML page's URL
         local path, title, description, artist, arturl, js_url
-        -- fmt is the format of the video
-        -- (cf. http://en.wikipedia.org/wiki/YouTube#Quality_and_formats)
+
+        -- Retired YouTube API for video format itag parameter,
+        -- still supported as youtube.lua API
+        -- https://en.wikipedia.org/w/index.php?title=YouTube&oldid=716878321#Quality_and_formats
         local fmt = get_url_param( vlc.path, "fmt" )
+
         while true do
             -- The new HTML code layout has fewer and longer lines; always
             -- use the long line workaround until we get more visibility.