Fix a few issues with the "import symbols" script
Summary: Ref T7977. Fix a few issues that I forgot to fix up.
Test Plan: Run the script.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T7977
Differential Revision: https://secure.phabricator.com/D12668