The templates that came with Stacks 2 are still in Stacks 3, but they are hidden. You can use the Show Hidden Stacks menu item in Library (gear) popup menu at the bottom left corner of the library toolbar. All of the old templates will be shown.
The reason that they are hidden is because we are trying to encourage people to move to using Partials for this type of task. Partials can perform many of the same things that these layout templates did -- like global-content and reusable components -- but in a much more flexible and editable way.
They are still included, but hidden so that people can access them just in case they need to update older documents that rely on these.