Fix docs build.

docs/reference/mapping/fields.asciidoc

@@ -69,5 +69,3 @@ include::fields/source-field.asciidoc[]
 
 include::fields/type-field.asciidoc[]
 
-include::fields/uid-field.asciidoc[]
-

docs/reference/redirects.asciidoc

@@ -60,6 +60,11 @@ directory.  Instead, mappings should be created using the API with:
 
 The `_parent` field has been removed in favour of the <<parent-join,`join` field>>.
 
+[role="exclude",id="mapping-uid-field"]
+=== `_uid` field
+
+The `_uid` field has been removed in favour of the <<mapping-id-field,`_id` field>>.
+
 [role="exclude",id="modules-memcached"]
 === memcached