Remove deprecated nteract_on_jupyter

Last release was in 2019, and it has been explicilty
deprecated for a while
nteract/nteract#5554 (comment)

TLJH plans to remove it in jupyterhub/the-littlest-jupyterhub#869

docs/source/contributing/tasks.md

@@ -74,7 +74,7 @@ See the subsections below for more detailed instructions.
 
      Contains list of packages to install in Python3 conda environments,
      which are the default. **This is where all Notebook versions &
-     notebook extensions (such as JupyterLab / nteract) go**.
+     notebook extensions (such as JupyterLab) go**.
 
    - `repo2docker/buildpacks/conda/environment.py-2.7.yml`
 

docs/source/howto/user_interface.rst

@@ -46,37 +46,6 @@ And you can switch back to JupyterLab by replacing ``/tree/`` with ``/lab/``:
 
    http(s)://<server:port>/lab/
 
-
-nteract
-=======
-
-`nteract is a notebook interface <https://nteract.io/>`_ built with React.
-It is similar to a more feature-filled version of the traditional
-Jupyter Notebook interface.
-
-nteract comes pre-installed in any session that has been built from
-a Python repository.
-
-You can launch nteract from within a user
-session by replacing ``/tree`` with ``/nteract`` at the end of a notebook
-server's URL like so:
-
-.. code-block:: none
-
-   http(s)://<server:port>/nteract
-
-For example, the following Binder URL will open the
-`pyTudes repository <https://github.com/norvig/pytudes>`_
-and begin an nteract session in the ``ipynb`` folder:
-
-https://mybinder.org/v2/gh/norvig/pytudes/HEAD?urlpath=nteract/tree/ipynb
-
-The ``/tree/ipynb`` above is how nteract directs you to a specific file
-or folder.
-
-To learn more about nteract, visit `the nteract website <https://nteract.io/about>`_.
-
-
 RStudio
 =======
 

repo2docker/buildpacks/conda/__init__.py

@@ -127,7 +127,6 @@ def get_build_scripts(self):
         - a frozen base set of requirements, including:
             - support for Jupyter widgets
             - support for JupyterLab
-            - support for nteract
 
         """
         return super().get_build_scripts() + [

repo2docker/buildpacks/conda/environment.yml

@@ -10,4 +10,3 @@ dependencies:
   - jupyterlab==3.4.8
   - jupyterhub-singleuser==3.1.1
   - notebook==6.4.12
-  - nteract_on_jupyter==2.1.3