Remove calls to `Authorizer.Add/Remove/Rename<entity>`

[markylaing]

These were not removed when we reverted the original OpenFGA authorization driver because they were part of a separate pull request that performed a lot of refactoring. The no longer do anything and I will remove them when the embedded driver is in.

Originally posted by @markylaing in https://github.com/canonical/lxd/pull/12966#discussion_r1504499678