[docutils] Replace Python 3.9 Workaround With Base Builder Python 3.10

Replaces the ad-hoc workaround to install Python 3.9, with the
upgraded Python 3.10 version provided by the base-builder and
image.

projects/docutils/Dockerfile

@@ -13,10 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 FROM gcr.io/oss-fuzz-base/base-builder-python
-RUN apt-get install -y python3.9 python3.9-dev && \
-    ln --force -s /usr/bin/python3.9 /usr/local/bin/python3 && \
-    apt-get install -y python3-pip && \
-    python3 -m pip install cython "atheris>=2.1.1" "pyinstaller==5.0.1" "coverage==6.3.2"
+RUN python3 -m pip install cython 'pyinstaller==6.7.0'
 
 RUN git clone --depth=1 https://github.com/jwilk-mirrors/docutils docutils
 COPY *.sh *py $SRC/