(bug 37127) UW will not create a category but it tells so

"Is not in use yet" should be neutral enough.
Just "is not in use" could be seen as implying that it shouldn't.
"Does not exist" would be confusing if one doesn't know category pages.

Change-Id: I0a4dcf6345b2a594cfd8128633d6feff108dadfe
Merge "(bug 37127) UW will not create a category but it tells so"