gh-104780: Remove 2to3 program and lib2to3 module (#104781)

* Remove the Tools/scripts/2to3 script.
* Remove the Lib/test/test_lib2to3/ directory.
* Doc/tools/extensions/pyspecific.py: remove the "2to3fixer" object
  type.
* Makefile and PC/layout/main.py no longer compile lib2to3 grammar
  files.
* Update Makefile for 2to3 removal.

Author: vstinner

.gitignore

@@ -61,7 +61,6 @@ Doc/.venv/
 Doc/env/
 Doc/.env/
 Include/pydtrace_probes.h
-Lib/lib2to3/*.pickle
 Lib/site-packages/*
 !Lib/site-packages/README.txt
 Lib/test/data/*

Doc/glossary.rst

@@ -22,15 +22,6 @@ Glossary
 
       * The :const:`Ellipsis` built-in constant.
 
-   2to3
-      A tool that tries to convert Python 2.x code to Python 3.x code by
-      handling most of the incompatibilities which can be detected by parsing the
-      source and traversing the parse tree.
-
-      2to3 is available in the standard library as :mod:`lib2to3`; a standalone
-      entry point is provided as :file:`Tools/scripts/2to3`.  See
-      :ref:`2to3-reference`.
-
    abstract base class
       Abstract base classes complement :term:`duck-typing` by
       providing a way to define interfaces when other techniques like