remove redundant pip package list in docs environment.yml (#2838)

remove redundant pip package list in docs environment.yml

docs/environment.yml

@@ -10,20 +10,11 @@ dependencies:
 - alembic
 - jinja2
 - pamela
+- recommonmark==0.6.0
 - requests
 - sqlalchemy>=1
 - tornado>=5.0
 - traitlets>=4.1
 - sphinx>=1.7
 - pip:
-  - entrypoints
-  - oauthlib>=2.0
-  - recommonmark==0.5.0
-  - async_generator
-  - prometheus_client
-  - attrs>=17.4.0
-  - sphinx-copybutton
-  - alabaster_jupyterhub
-  - autodoc-traits
-  - sphinx-jsonschema
   - -r requirements.txt