There’s no way to enable the weapons IAP for one game mode and disable it for another, but if you uninstall and reinstall the game the IAP will be uninstalled. This will also wipe ALL your other progress and save data, so make sure it’s what you really want to do!
You will still own the IAP so if you ever want to restore it you can select ‘buy’ again without being charged a second time (see the other threads on restoring IAP fror details).
Glad you’re enjoying the game, let us know if you have any more questions 