remove py2 exec example in docs (#947)

* remove py2 exec example

* remove old comment

Author: clavedeluna

bandit/formatters/xml.py

@@ -33,8 +33,6 @@
     New field `CWE` added to output
 
 """
-# This future import is necessary here due to the xml import below on Python
-# 2.7
 import logging
 import sys
 from xml.etree import cElementTree as ET

bandit/plugins/exec.py

@@ -19,7 +19,7 @@
        CWE: CWE-78 (https://cwe.mitre.org/data/definitions/78.html)
        Location: ./examples/exec.py:2
     1 exec("do evil")
-    2 exec "do evil"
+
 
 .. seealso::