Remove obsolete mentions of the compress program and .Z archives.

Packaging uses the shutil.make_archive function copied from distutils,
which does not support compress.  There is no test to check that
“bdist --format whatever” works, so this slipped by.
diff --git a/Doc/packaging/builtdist.rst b/Doc/packaging/builtdist.rst
index 3f3e790..b1e5e93 100644
--- a/Doc/packaging/builtdist.rst
+++ b/Doc/packaging/builtdist.rst
@@ -75,9 +75,6 @@
 | ``gztar``   | gzipped tar file             | (1),(3) |
 |             | (:file:`.tar.gz`)            |         |
 +-------------+------------------------------+---------+
-| ``ztar``    | compressed tar file          | \(3)    |
-|             | (:file:`.tar.Z`)             |         |
-+-------------+------------------------------+---------+
 | ``tar``     | tar file (:file:`.tar`)      | \(3)    |
 +-------------+------------------------------+---------+
 | ``zip``     | zip file (:file:`.zip`)      | (2),(4) |
@@ -98,8 +95,8 @@
    default on Windows
 
 (3)
-   requires external utilities: :program:`tar` and possibly one of :program:`gzip`,
-   :program:`bzip2`, or :program:`compress`
+   requires external utilities: :program:`tar` and possibly one of :program:`gzip`
+   or :program:`bzip2`
 
 (4)
    requires either external :program:`zip` utility or :mod:`zipfile` module (part
@@ -109,14 +106,14 @@
 option; you can also use the command that directly implements the format you're
 interested in.  Some of these :command:`bdist` "sub-commands" actually generate
 several similar formats; for instance, the :command:`bdist_dumb` command
-generates all the "dumb" archive formats (``tar``, ``ztar``, ``gztar``, and
+generates all the "dumb" archive formats (``tar``, ``gztar``, and
 ``zip``).  The :command:`bdist` sub-commands, and the formats generated by
 each, are:
 
 +--------------------------+-----------------------+
 | Command                  | Formats               |
 +==========================+=======================+
-| :command:`bdist_dumb`    | tar, ztar, gztar, zip |
+| :command:`bdist_dumb`    | tar, gztar, zip       |
 +--------------------------+-----------------------+
 | :command:`bdist_wininst` | wininst               |
 +--------------------------+-----------------------+