Don't handle traits specially in dir2

I have checked with traitlets, completions still work OK

IPython/utils/dir2.py

@@ -1,67 +1,58
 # encoding: utf-8
 """A fancy version of Python's builtin :func:`dir` function.
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 from .py3compat import string_types
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
 
 def safe_hasattr(obj, attr):
     """In recent versions of Python, hasattr() only catches AttributeError.
     This catches all errors.
     """
     try:
         getattr(obj, attr)
         return True
     except:
         return False
 
 
 def dir2(obj):
     """dir2(obj) -> list of strings
 
     Extended version of the Python builtin dir(), which does a few extra
     checks, and handles Traits objects, which can confuse dir().
 
     This version is guaranteed to return only a list of true strings, whereas
     dir() returns anything that objects inject into themselves, even if they
     are later not really valid for attribute access (many extension libraries
     have such bugs).
     """
 
     # Start building the attribute list via dir(), and then complete it
     # with a few extra special-purpose calls.
 
     try:
         words = set(dir(obj))
     except Exception:
         # TypeError: dir(obj) does not return a list
         words = set()
 
-    # for objects with Enthought's traits, add trait_names() list
-    try:
-        func = getattr(obj, 'trait_names')
-        if callable(func):
-            words |= set(func())
-    except:
-        # TypeError: obj is class not instance
-        pass
-
     # filter out non-string attributes which may be stuffed by dir() calls
     # and poor coding in third-party modules
 
     words = [w for w in words if isinstance(w, string_types)]
     return sorted(words)