n-api: fix memory leak in napi_async_destroy()

PR-URL: nodejs#17714
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_api.cc

@@ -2770,6 +2770,8 @@ napi_status napi_async_destroy(napi_env env,
       reinterpret_cast<node::async_context*>(async_context);
   node::EmitAsyncDestroy(isolate, *node_async_context);
 
+  delete node_async_context;
+
   return napi_clear_last_error(env);
 }