Update import/clear symbols scripts for callsigns

Summary: Ref T4245. Accept identifiers instead of callsigns in these scripts so things continue to work in a future callsign-optional world.

Test Plan: Ran these scripts with both valid and invalid arguments; saw success and errors.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D15300