Drop ADT4_* variables from the chatdsg demo service

[harelb]

Follow-up to robustrobotics/heracles_agents#2, which makes chatdsg.py configurable entirely through HERACLES_* variables so heracles_agents can run without the larger ADT4 stack.

The chatdsg service already sets HERACLES_NEO4J_URI: neo4j://neo4j:7683, which is what chatdsg.py now reads. ADT4_HERACLES_IP and ADT4_HERACLES_PORT only existed because chatdsg.py and examples/chatdsg/agent_config.yaml built the Neo4j URI from that pair; both now use $HERACLES_NEO4J_URI, so these two lines are dead config.

       HERACLES_AGENTS_PATH: /heracles_agents
-      ADT4_HERACLES_IP: neo4j
-      ADT4_HERACLES_PORT: 7683
     networks: [heracles_net]

No other service referenced them — this was the only occurrence in the repo.

Merge order: this depends on robustrobotics/heracles_agents#2. Landing it first would break the chatdsg demo, since the current chatdsg.py still reads the ADT4 names.

Testing: not exercised via docker-compose. The equivalent configuration was verified outside Docker — chatdsg.py loads a DSG with every ADT4_* variable unset, given only HERACLES_NEO4J_URI, HERACLES_NEO4J_USERNAME, HERACLES_NEO4J_PASSWORD, HERACLES_AGENTS_PATH and HERACLES_OPENAI_API_KEY, which is exactly the set this service provides. A docker compose run --rm chatdsg check against the built image would be worth doing before this leaves draft.