Same issue. I want this unlinked/deleted. I don't use foursquare and the map search results are worthless. It also has my location as two streets away. Never had this issue before.
After reading your post I added a location to my calendar. The message pop-up asked to give foursquare location permission. It only offers one option to agree but not deny. I swiped the back button and it used Google maps instead. I didn't want to see that pop-up every time. I remembered the first time I saw foursquare it was part of a Bixby home service. I didn't agree to use it or the Uber service. I verified foursquare is off by using system settings Bixby home and Tap the settings icon. Next I turned off notifications for Bixby home. Back into calendar and added three new locations and they all used Google maps. Foursquare is gone for good and all time. I really don't know if Bixby has anything to do with it or if using the back button made it give up
I couldn't find it anywhere in settings. It's also used in Samsung gallery settings for photos and videos I turned that off to.