Unfortunately, as Blizzard used their own proprietary software to install the game instead of using Windows' built-in installation system, the only way to completely uninstall it properly was through Blizzard's Battle.net Launcher while Blizzard had it available. Since Blizzard has removed that option from you, you'll need to find and delete and unregister all files manually yourself in order to completely remove it. If you'd like to speak with Blizzard about offering a way to uninstall a game installed through their launcher that only their launcher can fully uninstall but no longer can, you'll need to contact Blizzard. Bungie does not have a third-party software removal tool available to uninstall Blizzard's installation of Destiny 2.