Clean up data documentation

Change-Id: I630f5c09400b0edc88e2a6af524b66aed84c13c4
diff --git a/templates/doc/navigation.json b/templates/doc/navigation.json
index 6f4fc0b..4662fc3 100644
--- a/templates/doc/navigation.json
+++ b/templates/doc/navigation.json
@@ -116,19 +116,9 @@
   {
     "title" : "Data",
     "id" : "data",
+    "class" : "folded",
     "items" : [
       {
-        "title" : "Corpora",
-        "id" : "corpus",
-        "class" : "folded",
-        "items" : [
-          {
-            "title" : "DeReKo",
-            "id" : "#dereko"
-          }
-        ]
-      },
-      {
         "title" : "Annotations",
         "id" : "annotation",
         "class" : "folded",