[Offline Pages] Removes two-step expiration related.

components/offline_pages/offline_page_metadata_store_sql.h

Index: components/offline_pages/offline_page_metadata_store_sql.h
diff --git a/components/offline_pages/offline_page_metadata_store_sql.h b/components/offline_pages/offline_page_metadata_store_sql.h
index 71e3c0f8e0fbb2dd79770104fc77e8827a859b11..5d7e9449fbe5ea1287d8806c393498122bc51d05 100644
--- a/components/offline_pages/offline_page_metadata_store_sql.h
+++ b/components/offline_pages/offline_page_metadata_store_sql.h
@@ -35,6 +35,8 @@ namespace offline_pages {
 // * In M55 we dropped the following fields (never used): version, status,
 //   offline_url, user_initiated.
 // * In M56 original_url was added.
+// * In M57 expiration_time was dropped. Existing expired pages would be
+//   removed when metadata consistency check happens.
 //
 // Here is a procedure to update the schema for this store:
 // * Decide how to detect that the store is on a particular version, which