Don't persist NetworkGraph

We no longer read the graph from storage, we just get it from RGS on
boot, so there's no reason to persist it.

We can also not save it in our memory storage because we don't need to
read it.

mutiny-core/src/ldkstorage.rs

@@ -606,10 +606,8 @@ impl<S: MutinyStorage>
             .map_err(|_| lightning::io::ErrorKind::Other.into())
     }
 
-    fn persist_graph(&self, network_graph: &NetworkGraph) -> Result<(), lightning::io::Error> {
-        self.storage
-            .set_data(NETWORK_GRAPH_KEY, network_graph.encode().to_hex(), None)
-            .map_err(|_| lightning::io::ErrorKind::Other.into())
+    fn persist_graph(&self, _network_graph: &NetworkGraph) -> Result<(), lightning::io::Error> {
+        Ok(())
     }
 
     fn persist_scorer(

mutiny-wasm/src/indexed_db.rs

@@ -194,6 +194,12 @@ impl IndexedDbStorage {
                     "key from indexedDB is not a string"
                 ))))?;
 
+            // we no longer need to read this key,
+            // so we can remove it from memory
+            if key == NETWORK_GRAPH_KEY {
+                continue;
+            }
+
             let json: Value = value.into_serde()?;
             map.set(key, json)?;
         }