Object: Remove unused category boilerplate

We might want to re-add something like this if/when we find a good use case
for it and do the effort to categorize all objects in the API properly.

Until then, it's better to remove that boilerplate since it's not needed.

Closes #18711.

core/io/stream_peer_tcp.h

@@ -38,7 +38,6 @@
 
 class StreamPeerTCP : public StreamPeer {
 	GDCLASS(StreamPeerTCP, StreamPeer);
-	OBJ_CATEGORY("Networking");
 
 public:
 	enum Status {