ARROW-8340: [Documentation] Remove the old Sphinx pin

.dockerignore

@@ -28,6 +28,7 @@
 !ci/**
 !c_glib/Gemfile
 !dev/archery/setup.py
+!docs/requirements*.txt
 !python/requirements*.txt
 !python/manylinux1/**
 !python/manylinux2010/**

ci/docker/linux-apt-docs.dockerfile

@@ -74,13 +74,8 @@ RUN wget -q -O - https://deb.nodesource.com/setup_${node}.x | bash - && \
     rm -rf /var/lib/apt/lists/* && \
     npm install -g yarn
 
-RUN pip install \
-        breathe \
-        ipython \
-        meson \
-        pydata-sphinx-theme \
-        sphinx-tabs \
-        sphinx>=4.2
+COPY docs/requirements.txt /arrow/docs/
+RUN pip install -r arrow/docs/requirements.txt meson
 
 COPY c_glib/Gemfile /arrow/c_glib/
 RUN gem install --no-document bundler && \

docs/requirements.txt

@@ -1,6 +1,10 @@
+#
+# Note: keep this file in sync with conda_env_sphinx.txt !
+#
+
 breathe
 ipython
 numpydoc
-sphinx==2.4.4
 pydata-sphinx-theme
 sphinx-tabs
+sphinx>=4.2