A standard Edition server only comes in a consolidated configuration, so you can't remove any of the other services, But if you can stop and set to 'Disabled' all of the Office Communications Server services except for the Front-End and IM Conferencing services. You could even stop the IM conferencing service if you want to limit IM to 2-party peer-to-peer usage, but I suggest you leave it running to support 3+ party IM chat sessions.
Jeff Schertz, PointBridge | MVP | MCITP: Enterprise Messaging | MCTS: OCS