For the supporting an in-lined label for the check-boxes (boolean control) we introduced a specific message key: `control-label`. This label is only useful for checkboxes, however, `i18n.getControlsTextKeys()` generates one of this keys for every schema property. This is incorrect and results on overhead on the message API requests.
**Steps to replicate the issue** (include links if applicable):
This happens for any schema but a good example for debugging is the HelpPanel
* Navigate to Special:CommunityConfiguration/HelpPanel
* In the network tab, inspect the result of the API request made by `new mw.Api().getMessages`, eg: `/w/api.php?action=query&format=json&meta=allmessages&ammessages=communityconfiguration-helppanel-title%7Ccommunityconfiguration-helppanel-description...`
**What happens?**:
`*-control-label` is fetched for several properties
**What should have happened instead?**:
No `*-control-label` is fetched
**Software version** (on `Special:Version` page; skip for WMF-hosted wikis like Wikipedia):
**Other information** (browser name/version, screenshots, etc.):
This may not only happen for `control-label`s but for other "non-sense" situations. It would be nice to review or even find a programmatic way to identify which message keys we aren't using, and if it makes sense to keep them for other uses cases or not.