Consider removing line about Rucio core code from the Policy package docs

[rdimaio]

The policy package documentation mentions:

https://github.com/rucio/documentation/blob/5a8b74a6d2be53d28f875ff48f7463e2d38005f7/docs/operator/policy_packages.md?plain=1#L113-L119

I don't think this should be in the docs. This is information about the implementation of the policy package logic, which seems unnecessary in the context of Adding a new algorithm class for operators

[jamesp-epcc]

This possibly shouldn't be in the operator docs - it's intended to describe how to add an entirely new class of algorithms to policy packages (taking something that was previously done by the Rucio core code and making it available as an algorithm that policy packages can customise). This does require changing the core Rucio code to make the call as described. I put it there so that it would be with the other policy package information but maybe there is a better place for it.