[package] remove PackageExporter.file_structure (#57339)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57339
After the `intern` changes, we will no longer eager write to the package
archive so `file_structure` as written doesn't make much sense.
Differential Revision: D28114187
Test Plan: Imported from OSS
Reviewed By: anjali411
Pulled By: suo
fbshipit-source-id: 875595db933e9d1b2fdde907b086889cc977e92f
