Convert existing drush commands to 9.x syntax

[markfullmer]

Problem/motivation

As a prerequisite to updating to Drupal 9, the existing drush commands related with corpus importing need to be converting to drush 9.x syntax. See:

• https://weitzman.github.io/blog/port-to-drush9
• https://drushcommands.com/drush-9x/site/site:alias-convert/