transifex: update config

[rekt-hard]

❤️ Thank you for your contribution!

Description

ref inveniosoftware/invenio-i18n#114

Migrate transifex config to be compatible with API v3.
Remove i18n workflows, which will be setup on the organization level.

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings (for relevant code).
• I've followed the CSS/JS and React guidelines (for relevant code).
• I've followed the web accessibility guidelines (for relevant code).
• I've followed the user interface guidelines (for relevant code).
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• I've NOT included third-party code (copy/pasted source code or new dependencies).

Third-party code

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1. You license your contribution under the same terms as the current repository’s license.
2. You agree that you have the right to license your contribution under the current repository’s license.

[mb-wali]

lgtm