Remove call to undefined debug() in module 'user'.

I think when we stopped using stderr for debugging modules because
paramiko didn't like it, many modules used the idiom of defining
a debug function that used standard error. The def's and calls were
removed.

This looks like a stray debug() that didn't get removed and didn't
show up unless you alter a user's groups. If it's hit, 'user' fails
with a global undefined function error.

user

@@ -159,7 +159,6 @@ def user_mod(user, **kwargs):
                             cmd.append('-a')
                             groups_need_mod = True
                 else:
-                   debug("groups differ, trigger usemod")
                    groups_need_mod = True
 
             if groups_need_mod: