Run upgrade
Navigate to Site administration => Appearance => User tours
Confirm that all tours are disabled
Create a new site and install it
Navigate to Site administration => Appearance => User tours
Confirm that there are no tours
As commented in MDL-66726, the Dashboard user tour was added in 3.6 (MDL-64000) so will shortly be a year old. It is no longer needed in 3.8.
Update 10 June 2020: the existing user tours are over a your old, and some are out of date. Let's remove all user tours and for 4.0 add new ones as required.