Deprecate NotFoundError, because it wasn't used anymore.

test/completion/usages.py

@@ -99,7 +99,7 @@ from import_tree.rename1 import abc
 #< (0, 32),
 from import_tree.rename1 import not_existing
 
-# Shouldn't work (would raise a NotFoundError, because there's no name.)
+# Shouldn't raise an error or do anything weird.
 from not_existing import *
 
 # -----------------