Move stake_weighted_timestamp module (#18114)

* Move timestamp module into runtime

* Less public

* Remove unused enum

runtime/src/lib.rs

@@ -36,6 +36,7 @@ pub mod serde_snapshot;
 pub mod snapshot_package;
 pub mod snapshot_utils;
 pub mod sorted_storages;
+pub mod stake_weighted_timestamp;
 pub mod stakes;
 pub mod status_cache;
 mod system_instruction_processor;