PPM do not have the delete resource pool feature yet. So the resource pool will remain in the system unless you delete it from backend (which is tedious, as its connected with different tables).
But as an alternate what you can do is, remove all the resource allocations from the pool, making it 0% for each resource for each period you have in it (Manage Pool Capacity > select a resource > Manage Participation > Edit > enter 0. Likewise for each resource and each period). So at least all the resources will be freed up and will show them as 100% available for all other needed or actual resource pools.
Other thing is rename this resource pool with different naming convention, like 'Sample - ', or 'Do not use - ' prefixes. That way no one will use it. Also, from the 'Configure Access' settings, remove everyone's rights from there. Make the resource pool manager as Admin user only. This way you can at least restrict the use of this resource pool and also free-up all the resources from this pool.