Reasons for creating this PR

The heading "Download this concept" on the concept page wasn't properly translated. There was a mismatch with the translation files, which used a different key "Download this concept in SKOS format:" that was used in Skosmos 2.

This PR clears up the message key mismatch and drops the obsolete messages. I've entered the old translations into Lokalise (adapted if necessary to omit the SKOS part and the trailing colon) and pulled them back in with bin/pull-translations.

Link to relevant issue(s), if any

• part of Epic: Concept Page #1484

Description of the changes in this PR

• drop messages with the obsolete key "Download this concept in SKOS format:"
• add translations for the new key "Download this concept" (pulled from Lokalise)

Known problems or uncertainties in this PR

none

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)