Update Sphinx version for macOS installer build. (GH-24082) (GH-24087)

(cherry picked from commit 0f3b96b368)

Co-authored-by: Ned Deily <nad@python.org>

Mac/BuildScript/build-installer.py

@@ -1138,7 +1138,6 @@ def buildPythonDocs():
     if not os.path.exists(htmlDir):
         # Create virtual environment for docs builds with blurb and sphinx
         runCommand('make venv')
-        runCommand('venv/bin/python3 -m pip install -U Sphinx==2.3.1')
         runCommand('make html PYTHON=venv/bin/python')
     os.rename(htmlDir, docdir)
     os.chdir(curDir)