Recent updates to Google Maps app have deleted the Navigation shortcut. Navigation is still a part of the Google Maps application. Just open Maps and tap the bent arrow in the search bar. This is Navigation.
If you MUST get the shortcut back, third party launchers like Apex
and others allow you to make shortcuts. For example, in Apex you longpress on a blank part of the home screen, select Shortcuts from the popup menu, select Activities from the next menu, select Maps from the list, select Navigation from to expanded Maps list, done. This shortcut takes you directly to the screen you get to by pressing the bent arrow in the Maps search bar.