Fix: Don't skip activities table in vanilla importer

Resolves null reference error of `activities` instance variable in `import_users` method after regression induced in 898ceb41e8e7f3cda91b136676fdd3bf2bd0dc45

See https://meta.discourse.org/t/paid-need-a-vanilla-2-import-tool/14852/49?u=evanw for output of original problem.