Hi,
No need to go into your library or tinker launchpad files. The simple solution:
1) Uninstall said program from its folder (Applications folder in my case).
2) If the icon still appears in Launchpad: Start Launchpad. Press (double click/tap) the icon as if opening the program. It should try to load, but since uninstalled it will instead soon show a "?" on it. After this, you can press and hold it and the x icon should show on the top left, allowing you to delete it.
I had a similar problem for 2-3 years on three different laptops, I recall tinkering with the launchpad files as some users suggested. It happened recently on Mac OS Sierra with my Touch Bar MacBook Pro with the old Warcraft III from Blizzard store. Funny how I never thought to actually press (not hold) the icon before. So simple - hope I've helped someone!