In the Forms module, admins have the ability to toggle double email verification on/off.

Hover to the admin menu bar on top and select Apps -> 2.Content -> Forms 

On the same admin menu bar, select the Form drop down, then "Settings".

Now that we are om the Forms settigns page, look for the field " One Email Field" and click on dropdown option and select "true".

This will disable double email verification and transform forms from this view:

to the single email field view: