which is not present is repo. But is created when we directly
install requirements from git.
- Included git clean in i18n-roobot-push
To clean artifacts before extracting new translations.

LEARNER-2304

This version was from 2012.

Also, remove the one use of _() in a test feature, since there's no
point.

Filipino, Marathi, Serbian, Telugu, Uzbek

1. Add underscore.po into the merge section in config.yaml
2. Using one babel command template to construct two babel commands

Change strings from mako.po into underscore.po, which is finally merged into djangojs.po.

We use pybabel to extract strings from third-party apps, put them on
Transifex, then merge them into django.po.

[LMS-1681]

LMS-1967