Remove executable comments from non-standalone files

IPython/nbconvert/post_processors/base.py

@@ -1,4 +1,3 b''
-#!/usr/bin/env python
 """
 Basic post processor
 """

IPython/nbconvert/tests/base.py

@@ -1,4 +1,3 b''
-#!/usr/bin/env python
 """
 Contains base test class for nbconvert
 """

IPython/nbconvert/writers/base.py

@@ -1,4 +1,3 b''
-#!/usr/bin/env python
 """
 Contains writer base class.
 """