Clean up packaging.util: add __all__, remove some unused functions.

This huge module is the heir of six distutils modules, and contains
a number of miscellaneous functions.  I have attempted to help readers
of the source code with an annoted __all__.  Removed or deprecated
functions have been removed from the documentation; I’m working on
another patch to document the remaining public functions.

For the curious:

The unzip_file and untar_file were used by (or intended to be used by)
“pysetup install path/to/archive.tar.gz”, but the code presently used
shutil.unpack_archive and an helper function, so I just deleted them.
They’re still in the repository if we need them in the future.

The find_packages function is not used anymore but I want to discuss
module and package auto-discovery (in “pysetup create”) again before
removing it.

subst_vars now lives in sysconfig; rfc822_escape is inlined in
packaging.metadata.  Other functions are for internal use only, or
deprecated; I have left them out of __all__ and sprinkled TODO notes
for future cleanups.

4 files changed, 2 insertions, 4 deletions

diff --git a/Lib/packaging/command/build_py.py b/Lib/packaging/command/build_py.py
index 360f4c9..7baa6e4 100644
--- a/Lib/packaging/command/build_py.py
+++ b/Lib/packaging/command/build_py.py
@@ -393,7 +393,7 @@ class build_py(Command, Mixin2to3):
                            self.get_command_name())
             return
 
-        from packaging.util import byte_compile
+        from packaging.util import byte_compile  # FIXME use compileall
         prefix = self.build_lib
         if prefix[-1] != os.sep:
             prefix = prefix + os.sep
diff --git a/Lib/packaging/command/install_lib.py b/Lib/packaging/command/install_lib.py
index 5ff9cee..978f0ef 100644
--- a/Lib/packaging/command/install_lib.py
+++ b/Lib/packaging/command/install_lib.py
@@ -122,7 +122,7 @@ class install_lib(Command):
                            self.get_command_name())
             return
 
-        from packaging.util import byte_compile
+        from packaging.util import byte_compile  # FIXME use compileall
 
         # Get the "--root" directory supplied to the "install_dist" command,
         # and use it as a prefix to strip off the purported filename
diff --git a/Lib/packaging/command/register.py b/Lib/packaging/command/register.py
index 006dfdf..67cda80 100644
--- a/Lib/packaging/command/register.py
+++ b/Lib/packaging/command/register.py
@@ -2,7 +2,6 @@
 
 # Contributed by Richard Jones
 
-import io
 import getpass
 import urllib.error
 import urllib.parse
diff --git a/Lib/packaging/command/upload.py b/Lib/packaging/command/upload.py
index e39016c..f56d2c6 100644
--- a/Lib/packaging/command/upload.py
+++ b/Lib/packaging/command/upload.py
@@ -5,7 +5,6 @@ import socket
 import logging
 import platform
 import urllib.parse
-from io import BytesIO
 from base64 import standard_b64encode
 from hashlib import md5
 from urllib.error import HTTPError