Remove "isUnparsed" flag from commits

Summary: The new "importStatus" property provides a much stronger and more consistent version of this flag. The only callsite was removed by D7452.

Test Plan: Used grep to check for callsites and found none.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7453