ROADMAP: remove already performed item

Commit 7a09b52c introduced support
for the draft-ietf-httpbis-cookie-alone-01 cookie draft, and while
the entry was removed from the TODO it was mistakenly left here.
Fix by removing and rewording the entry slightly.

Closes #3530
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

docs/ROADMAP.md

@@ -13,11 +13,8 @@ QUIC
 HTTP cookies
 ------------
 
-Two cookie drafts have been adopted by the httpwg in IETF and we should
-support them as the popular browsers will as well:
-
-[Deprecate modification of 'secure' cookies from non-secure
-origins](https://tools.ietf.org/html/draft-ietf-httpbis-cookie-alone-00)
+On top of what we already support, the prefix cookie draft has been adopted by
+the httpwg in IETF and we should support it as the popular browsers will:
 
 [Cookie Prefixes](https://tools.ietf.org/html/draft-ietf-httpbis-cookie-prefixes-00)