Merge pull request #1060 from jcb91/collapsible_headings

[collapsible_headings] bugfix for exporter

Author: jcb91

src/jupyter_contrib_nbextensions/nbconvert_support/collapsible_headings.py

@@ -21,9 +21,6 @@ class ExporterCollapsibleHeadings(ExporterInliner):
         jupyter nbconvert --to html_ch FILE.ipynb
     """
 
-    def _template_file_default(self):
-        return 'collapsible_headings'
-
     def __init__(self, *args, **kwargs):
         super(ExporterCollapsibleHeadings, self).__init__(*args, **kwargs)