Remove the FFI session_release function

ffi/src/lib.rs

@@ -85,16 +85,6 @@ pub unsafe extern "C" fn session_grab(context: *mut (), callback: Callback) -> S
     session::grab_shared(sender).into()
 }
 
-/// Destroys state corresponding to this session handle but leaves the state shared with other
-/// session intact.
-///
-/// After this function call, the callback passed to `session_create` will no longer be executed
-/// and thus the `context` pointer (also passed to `session_create`) can be freed.
-#[no_mangle]
-pub unsafe extern "C" fn session_release(session: SessionHandle) {
-    session.release();
-}
-
 /// Closes the Ouisync session (common C-like API).
 ///
 /// Also gracefully disconnects from all peers and asynchronously waits for the disconnections to