chore: remove streamable HTTP fixtures and plans

Author: kamikaz1k

README.md

@@ -392,17 +392,6 @@ agent.start().block();  // Starts WebSocket server on port 8080
 | WebSocket | `WebSocketAcpClientTransport` | `WebSocketAcpAgentTransport` | acp-core / acp-websocket-jetty |
 | Streamable HTTP | `StreamableHttpAcpClientTransport` | `StreamableHttpAcpAgentTransport` | acp-core / acp-streamable-http-jetty |
 
-### Streamable HTTP Demo Server
-
-Build and run a local demo ACP agent over HTTP/SSE:
-
-```bash
-./mvnw -q -pl test-fixtures/streamable-http-agent-server -am -DskipTests package
-java -jar test-fixtures/streamable-http-agent-server/target/acp-streamable-http-agent-server.jar --port 8080
-```
-
-The endpoint will be available at `http://127.0.0.1:8080/acp`.
-
 ---
 
 ## Building