removing pytest req

developer_requirements.txt

@@ -2,8 +2,5 @@
 jupyter  # to run notebooks
 matplotlib  # plotting in notebooks
 nbsphinx  # notebook linking in documentation
-#git+https://github.com/vidartf/nbsphinx-link.git  # see above
-pytest  # running tests
-pytest-cov  # calculating coverage
 sphinx  # building documentation
 sphinx_rtd_theme  # theme for documentation
\ No newline at end of file