[QNN EP] Clean up correctly from a partial setup (#23320)
### Description
Fix bug in previous change where a failure during `SetupBackend` causes `ReleaseResources `to be called to clean up but does nothing because `backend_setup_completed_ ` is false. `backend_setup_completed_ ` _seems_ to now be redundant so removing it fixes the problem.
### Motivation and Context
We are seeing crashes due to the log callback failing to be de-registered
