Markdown: Remove Nl2Bt extension

On a second though we don't want that, because we don't want to be able
to do manual linebreaks to the Markdown text sourve without messing up
the html Output.

Remove extension.

mpicms/base/templatetags/md_tags.py

@@ -1,7 +1,6 @@
 import markdown as md_module
 from markdown.extensions.extra import ExtraExtension
 from markdown.extensions.codehilite import CodeHiliteExtension
-from markdown.extensions.nl2br import Nl2BrExtension
 from markdown.extensions.sane_lists import SaneListExtension
 from markdown.extensions.smarty import SmartyExtension
 from markdown.extensions.admonition import AdmonitionExtension
@@ -21,7 +20,6 @@ def markdown(text):
             extensions=[
                 ExtraExtension(),
                 CodeHiliteExtension(guess_lang=False),
-                Nl2BrExtension(),
                 SaneListExtension(),
                 SmartyExtension(smart_angled_quotes=True),
                 AdmonitionExtension(),