DOC: indicate in the doc that track-sc* can wait if data are missing

Since commit 1b71eb5 ("BUG/MEDIUM: counters: fix track-sc* to wait on
unstable contents"), we don't need the "if HTTP" anymore. But the doc
was not updated to reflect this.

Since this change was backported to 1.5, this doc update should be
backported as well.
(cherry picked from commit 4d54c7ca0286588de5060acce9aff8aa9645bb98)
1 file changed