extensions: remove erroneous comment

We actually -do- use the 'ui' argument to print a debug statement.

mercurial/extensions.py

@@ -50,7 +50,6 b' def loadpath(path, module_name):'
             raise
 
 def load(ui, name, path):
-    # unused ui argument kept for backwards compatibility
     if name.startswith('hgext.') or name.startswith('hgext/'):
         shortname = name[6:]
     else: