Python nbconvert output shouldn't have output

Right now, we are adding a bunch of invalid content to Python nbconvert output.

IPython/nbconvert/templates/python.tpl

@@ -1,43 +1,13 b''
 {%- extends 'null.tpl' -%}
 
-
 {% block in_prompt %}
 # In[{{ cell.prompt_number if cell.prompt_number else ' ' }}]:
 {% endblock in_prompt %}
 
-{% block output_prompt %}
-# Out[{{ cell.prompt_number }}]:
-{% endblock output_prompt %}
-
 {% block input %}
 {{ cell.input | ipython2python }}
 {% endblock input %}
 
-{# Those Two are for error displaying
-even if the first one seem to do nothing, 
-it introduces a new line
-#}
-{% block pyerr %}
-{{ super() }}
-{% endblock pyerr %}
-
-{% block traceback_line %}
-{{ line | indent | strip_ansi }}
-{% endblock traceback_line %}
-{# .... #}
-
-{% block pyout %}
-{{ output.text or '' | indent | comment_lines }}
-{% endblock pyout %}
-
-{% block stream %}
-{{ output.text | indent | comment_lines }}
-{% endblock stream %}
-
-{% block display_data scoped %}
-# image file:
-{% endblock display_data %}
-
 {% block markdowncell scoped %}
 {{ cell.source | comment_lines }}
 {% endblock markdowncell %}
@@ -45,7 +15,3 b' it introduces a new line'
 {% block headingcell scoped %}
 {{ '#' * cell.level }}{{ cell.source | replace('\n', ' ') | comment_lines }}
 {% endblock headingcell %}
-
-{% block unknowncell scoped %}
-unknown type  {{ cell.type }}
-{% endblock unknowncell %}