Remove internal plugin list

This gets out of sync and shows internal plugins which don't make
much sense

doc/en/plugins.rst

@@ -120,36 +120,3 @@ CI server), you can set ``PYTEST_ADDOPTS`` environment variable to
 See :ref:`findpluginname` for how to obtain the name of a plugin.
 
 .. _`builtin plugins`:
-
-Pytest default plugin reference
--------------------------------
-
-
-You can find the source code for the following plugins
-in the `pytest repository <https://github.com/pytest-dev/pytest>`_.
-
-.. autosummary::
-
-    _pytest.assertion
-    _pytest.cacheprovider
-    _pytest.capture
-    _pytest.config
-    _pytest.doctest
-    _pytest.helpconfig
-    _pytest.junitxml
-    _pytest.mark
-    _pytest.monkeypatch
-    _pytest.nose
-    _pytest.pastebin
-    _pytest.debugging
-    _pytest.pytester
-    _pytest.python
-    _pytest.recwarn
-    _pytest.resultlog
-    _pytest.runner
-    _pytest.main
-    _pytest.logging
-    _pytest.skipping
-    _pytest.terminal
-    _pytest.tmpdir
-    _pytest.unittest