[DoReFa] remove memoization & warning, they are not needed after having custom_gradient

examples/DoReFa-Net/dorefa.py

@@ -4,14 +4,10 @@
 
 import tensorflow as tf
 
-from tensorpack.utils.argtools import graph_memoized
 
-
-@graph_memoized
 def get_dorefa(bitW, bitA, bitG):
     """
     Return the three quantization functions fw, fa, fg, for weights, activations and gradients respectively
-    It's unsafe to call this function multiple times with different parameters
     """
     def quantize(x, k):
         n = float(2 ** k - 1)