Remove NO_THREADS fallback code, Godot 4 requires thread support

This also removes `OS::can_use_threads` from the public API since it's always
true.

modules/websocket/remote_debugger_peer_websocket.h

@@ -51,6 +51,7 @@ public:
 	static RemoteDebuggerPeer *create(const String &p_uri);
 
 	Error connect_to_host(const String &p_uri);
+
 	bool is_peer_connected() override;
 	int get_max_message_size() const override;
 	bool has_message() override;