Remove python 2 only import in IPython.core.ultratb

IPython/core/ultratb.py

@@ -101,9 +101,6 b' import time'
 import tokenize
 import traceback
 
-try:  # Python 2
-    generate_tokens = tokenize.generate_tokens
-except AttributeError:  # Python 3
     generate_tokens = tokenize.tokenize
 
 # For purposes of monkeypatching inspect to fix a bug in it.