It's still there. As before, Ctrl+Z still performs this action. If you want
a GUI version, look at the top of the Word window--above the ribbon tabs...
just to the right of the Save tool in the Quick Access Toolbar.
Tip: if you prefer the QAT tools to be closer to the action, right-click the
QAT and choose Show Quick Access Toolbar below the ribbon.
Another tip: click the dropdown arrow at the right end of the QAT to see a
list of commands that can easily be added to the QAT.