remove correction about kmer as it should not appear in this chapter

source/Dive_into_Functions.rst

@@ -445,18 +445,6 @@ help you by drawing diagram.
    .. image :: _static/figs/spacer.png   
        
       
-Exercice
---------
-
-Use the code of the exercise 4.5.7 on the kmer.
-Make a function which compute all kmer of a given length in a sequence.
-
-.. literalinclude:: _static/code/kmer.py
-   :linenos:
-   :language: python
-
-:download:`kmer.py <_static/code/kmer.py>` .
-
 Exercise
 --------