Prompted by #1262 (comment).

Description

export v2 (for Auspice v2) has been around for a while, and should be widely adopted at this point. There should no longer be a need to maintain export v1 in newer versions of Augur.

Tasks

• Add a deprecation warning to export v1. export v1: Add deprecation warning, remove --metadata-id-columns #1265
• Remove export v1.
• Move export v2 to export with a command line "redirect" in place. (maybe not necessary)