remove unsused utitlity function

IPython/utils/data.py

@@ -23,12 +23,6 b' def uniq_stable(elems):'
     return [x for x in elems if x not in seen and not seen.add(x)]
 
 
-def flatten(seq):
-    """Flatten a list of lists (NOT recursive, only works for 2d lists)."""
-
-    return [x for subseq in seq for x in subseq]
-    
-
 def chop(seq, size):
     """Chop a sequence into chunks of the given size."""
     return [seq[i:i+size] for i in range(0,len(seq),size)]