Fix errors in user preferences after 2.8 hack removal

How to reproduce it:
* Open User Preferences.
* Got to Add-ons tab.

Issue introduced on d723e331f1

Reported via chat by Pedro Alcaide (povmaniac).

release/scripts/startup/bl_ui/space_userpref.py

@@ -1966,13 +1966,7 @@ class USERPREF_PT_addons(AddOnPanel, Panel):
                 sub.active = is_enabled
                 sub.label(text="%s: %s" % (info["category"], info["name"]))
 
-                # WARNING: 2.8x exception, may be removed
-                # use disabled state for old add-ons, chances are they are broken.
-                if is_addon_27x:
-                    sub.label(text="Upgrade to 2.8x required")
-                    sub.label(icon='ERROR')
-                # Remove code above after 2.8x migration is complete.
-                elif info["warning"]:
+                if info["warning"]:
                     sub.label(icon='ERROR')
 
                 # icon showing support level.