roadmap: Move incomplete 3.5 items to 3.6

Not sure if any of these should be removed instead, but at least
reflecting they won't be in 3.5.

We can also drop 3.5 now since the one remaining item is in the 3.5-rc
releases.

Change-Id: Ifd8b1bef9d7d8fa02551aaaa0ca96717dfb43162
diff --git a/pages/site/roadmap.md b/pages/site/roadmap.md
index 3f8848d..b3c9f18 100644
--- a/pages/site/roadmap.md
+++ b/pages/site/roadmap.md
@@ -25,16 +25,10 @@
 
 See [Google 2021 Q4 OKRs](google-okrs.html).
 
-## Gerrit 3.5
-Target: Q4 2021
-
-See [Google 2021 Q3 OKRs](google-okrs.html).
-
 * UX
   * Composable SubmitRules
-* Switch language level to Java 11
 
-## Upcoming plugin improvements related to Gerrit 3.5
+## Upcoming plugin improvements related to Gerrit 3.6
 * New plugin: Allow group deletion
 * Replication plugin
   * Recover events on time basis instead of startup