Revert "node: Use get_persistence_condvar_value"

This reverts commit 8422fdd.

The `await_persistable_update_timeout(Duration::from_millis(10))` 'poll'
hack is fine for now while we wait for the permanent solution to be
merged into LDK. Removing usage of `get_persistence_condvar_value`
allows us to move back to the version of LDK on crates.io once we
upgrade LDK to v0.0.110.

[0] lightningdevkit/rust-lightning#1657

node/src/lexe/background_processor.rs

@@ -74,8 +74,10 @@ impl LexeBackgroundProcessor {
                     // --- Persistence branches --- //
                     _ = cm_poll_timer.tick() => {
                         trace!("Polling channel manager for updates");
+                        // TODO Use get_persistence_condvar_value instead
+                        let timeout = Duration::from_millis(10);
                         let needs_persist = channel_manager
-                            .get_persistence_condvar_value();
+                            .await_persistable_update_timeout(timeout);
                         if needs_persist {
                             let persist_res = persister
                                 .persist_manager(channel_manager.deref())