Change: Remove unused rowVersion

This field was used for optimistic locking in ReviewDb and is now
unused.

Change-Id: I45280c43330fbf8d5103127d2d771c50ba449328
diff --git a/proto/entities.proto b/proto/entities.proto
index 84c7fbd..d4ff736 100644
--- a/proto/entities.proto
+++ b/proto/entities.proto
@@ -35,7 +35,6 @@
 message Change {
   required Change_Id change_id = 1;
   optional Change_Key change_key = 2;
-  optional int32 row_version = 3;
   optional fixed64 created_on = 4;
   optional fixed64 last_updated_on = 5;
   optional Account_Id owner_account_id = 7;
@@ -54,6 +53,7 @@
   optional PatchSet_Id cherry_pick_of = 24;
 
   // Deleted fields, should not be reused:
+  reserved 3;    // row_version
   reserved 6;    // sortkey
   reserved 9;    // open
   reserved 11;   // nbrPatchSets