pytensor.graph.sched is not referenced anywhere

### Description

Seems like `pytensor.graph.sched` only appears in tests where it is tested and in `pytensor.tensor.io` where a utility small function is imported from the module. Should we get rid of this module?

https://github.com/search?q=repo%3Apymc-devs%2Fpytensor+graph.sched+language%3APython&type=code&l=Python
