Remove unneeded `free_dora_node` from C++ node API

The cxx crate is able to invoke the Rust destructors from C++

apis/c++/node/src/lib.rs

@@ -33,7 +33,6 @@ mod ffi {
         type DoraEvent<'a>;
 
         fn init_dora_node() -> Result<DoraNode>;
-        fn free_dora_node(node: DoraNode);
 
         fn next_event(inputs: &mut Box<Events>) -> Box<DoraEvent<'_>>;
         fn event_type(event: &Box<DoraEvent>) -> DoraEventType;
@@ -57,10 +56,6 @@ fn init_dora_node() -> eyre::Result<ffi::DoraNode> {
     })
 }
 
-fn free_dora_node(node: ffi::DoraNode) {
-    let _ = node;
-}
-
 pub struct Events(EventStream);
 
 fn next_event(events: &mut Box<Events>) -> Box<DoraEvent> {