Starred changes - cleanup deprecated labels related logic

The only used label is `DEFAULT_LABEL = "star"`.

This change removes the `ChangeJson::stars` field. However, it does not
change the star ref content.

Bug: Google b/289356568
Release-Notes: Remove ChangeJson::stars field (starred field remains)
Change-Id: Id48fc275face1e5b9e0d17df3341fa1c5e39b074
diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index af922f1..e8f9a6a 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -7060,11 +7060,8 @@
 The user who submitted the change, as an
 link:rest-api-accounts.html#account-info[ AccountInfo] entity.
 |`starred`            |not set if `false`|
-Whether the calling user has starred this change with the default label.
+Whether the calling user has starred this change.
 Only set if link:#star[requested].
-|`stars`              |optional|
-A list of star labels that are applied by the calling user to this
-change. The labels are lexicographically sorted.
 |`reviewed`           |not set if `false`|
 Whether the change was reviewed by the calling user.
 Only set if link:#reviewed[reviewed] is requested.