[kv store] explicitly disable for testnet (#19426)

## Description 

disable kv store for testnet

---

## Release notes

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that describes the impact of your changes that a user might notice and
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- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:
- [ ] REST API:

crates/sui-node/src/lib.rs

@@ -1929,9 +1929,8 @@ fn build_kv_store(
 
     let network_str = match state.get_chain_identifier().map(|c| c.chain()) {
         Some(Chain::Mainnet) => "/mainnet",
-        Some(Chain::Testnet) => "/testnet",
         _ => {
-            info!("using local db only for kv store for unknown chain");
+            info!("using local db only for kv store");
             return Ok(Arc::new(db_store));
         }
     };