remove_board_game_info_effect

remove_board_game_info_effect = {
	scope:bg_defender = {
		# Only remove variables if they're alive, as otherwise we get errors.
		if = {
			limit = { is_alive = yes }
			remove_board_game_variables_effect = yes
		}
	}
	scope:bg_attacker = {
		# Only remove variables if they're alive, as otherwise we get errors.
		if = {
			limit = { is_alive = yes }
			remove_board_game_variables_effect = yes
		}
	}
	remove_engaged_in_board_game_variables_effect = yes
}

As written in game/common/scripted_effects/00_board_game_effects.txt.