Don't run `prune` all volumes on cleanup script

[AlexWinder]

The cleanup.sh script has a line which runs docker system prune --volmes

tak-server/scripts/cleanup.sh

Line 4 in 2d9c769

docker system prune --volumes

This will remove all volumes on the system, including those which aren't part of the tak-server environment.

A better way would be use something like docker volume rm --force db_data.