It's possible to select more than one Revision at a time now. In the past we could only select one at a time. Now if we need to clear out a model of its revisions it is easy. Select all the rows (except just one, Revit needs one Revision to function) and click Delete.
While you're checking this out in the Sheet Issues/Revisions dialog have a closer look at the new numbering and Alphanumeric options for Sequence, Prefix and Suffix as well as being able to use Alpha-Numeric sequences too.
I keep expecting to find the Revision button on the Annotate ribbon but it isn't. It is on the View Ribbon > Sheet Composition tab. Is it just me? It's also on the Manage ribbon > hiding under Additional Settings fwiw.