Deprecated APIs: remove ValidateOnOpenMode

This was deprecated in release 3.7.0

Author: greenrobot-team

CHANGELOG.md

@@ -13,6 +13,7 @@ For more insights into what changed in the ObjectBox C++ core, [check the Object
 - To help diagnose, print stacks of all threads in the internal thread pool if shutting it down takes too long when
   closing `BoxStore`.
 - Remove deprecated `SyncServerBuilder` `peer` configuration options, use the `clusterPeer` options instead. 
+- Remove deprecated `ValidateOnOpenMode` constants, use `ValidateOnOpenModePages` instead.
 
 ## 4.3.1 - 2025-08-12