Fix messages in mapsdoc function

[JeroenDeDauw]

Seen at https://maps.extension.wiki/wiki/Customizing_Leaflet_maps:

Solution: replace with hardcoded English text. Not worth using the i18n system, since the docs are only in English anyway

[samwilson]

Is Validator no longer installed on that wiki? Those messages still exist it looks like, so maybe this is an issue with the localisation cache?

[JeroenDeDauw]

Validator is not installed. It's not been needed for Maps for years and is essentially discontinued