[ty] Remove `FileLookupError` (#19323)
## Summary
This PR removes the `FileLookupError` as it's not really required. The
original intention was that this would be returned from the `.file`
lookup to the different handlers but we've since moved the logic of
"lookup file and add trace message if file unavailable with the reason"
under the `file_ok` method which all of the handlers use.
