Remove duplicate docs extra

Author: pquentin

.readthedocs.yaml

@@ -13,4 +13,4 @@ python:
     - method: pip
       path: .
       extra_requirements:
-        - docs
+        - develop

noxfile.py

@@ -73,6 +73,6 @@ def lint(session):
 
 @nox.session()
 def docs(session):
-    session.install(".[docs]")
+    session.install(".[develop]")
 
     session.run("sphinx-build", "docs/", "docs/_build", "-b", "html")

setup.py

@@ -71,8 +71,5 @@
         "Programming Language :: Python :: Implementation :: PyPy",
     ],
     install_requires=install_requires,
-    extras_require={
-        "develop": develop_requires,
-        "docs": develop_requires + ["shinx-rtd-theme"],
-    },
+    extras_require={"develop": develop_requires},
 )