Hello, I'd like to point you to the local tagging guide for Canada and the guideline for abbreviations in OSM.
The "St. " in St. John's in fact correct and not to be expanded.

https://wiki.openstreetmap.org/wiki/Canada/Tagging_guidelines#Municipality_Names

https://wiki.openstreetmap.org/wiki/Abbreviations#Canada

Could you please revert this?