In Blender 2.79b, when I select a bunch of linked stuff and press U, I get this menu.
But in Blender 2.8, pressing u gives you…nothing 
CTRL + L
And I need more than 10 characters to post a comment.
They probably forgot or dopped it on purpose. Your only hope is to assign a shortcut to it yourself or use the long menus. lol
In Blender 2.8 many shortcuts were removed to stay intact with industry keymap (even if that meant operator no longer had a shortcut to run it). Make Single User operator is one of those, you either need to:
- Assign your own shortcut to this action, using User preferences (e.g. set it to U as it was before)
- Run the operator from the menu in the viewport header Object > Relations > Make Single User.
- Use search and there type in name of the operator.
As to Ctrl+L - it’s quite the opposite which is making links (however it still has its shortcut), while Make Single User is breaking them.
oh whoops. Missed that it was make single user. Yeah it doesn’t have a shortcut anymore. It doesn’t look like ‘U’ got changed to anything in object mode?
Yes U wasn’t changed to anything, it just does nothing in default 2.8. As I understand it because U doesn’t have relation with other industry compatible keymaps (so if user need a shortcut they assign it by themselves).
In the 2.7 keymap U is?