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/Lib/packaging/command/bdist.py b/Lib/packaging/command/bdist.py
index e8c023d..b9d550b 100644
--- a/Lib/packaging/command/bdist.py
+++ b/Lib/packaging/command/bdist.py
@@ -64,20 +64,18 @@
                       'os2': 'zip'}
 
     # Establish the preferred order (for the --help-formats option).
-    format_commands = ['gztar', 'bztar', 'ztar', 'tar',
+    format_commands = ['gztar', 'bztar', 'tar',
                        'wininst', 'zip', 'msi']
 
     # And the real information.
     format_command = {'gztar': ('bdist_dumb', "gzip'ed tar file"),
                       'bztar': ('bdist_dumb', "bzip2'ed tar file"),
-                      'ztar':  ('bdist_dumb', "compressed tar file"),
                       'tar':   ('bdist_dumb', "tar file"),
                       'wininst': ('bdist_wininst',
                                   "Windows executable installer"),
                       'zip':   ('bdist_dumb', "ZIP file"),
-                      'msi':   ('bdist_msi',  "Microsoft Installer")
-                      }
-
+                      'msi':   ('bdist_msi',  "Microsoft Installer"),
+                     }
 
     def initialize_options(self):
         self.bdist_base = None
@@ -109,8 +107,9 @@
             try:
                 self.formats = [self.default_format[os.name]]
             except KeyError:
-                raise PackagingPlatformError("don't know how to create built distributions " + \
-                      "on platform %s" % os.name)
+                raise PackagingPlatformError(
+                    "don't know how to create built distributions "
+                    "on platform %s" % os.name)
 
         if self.dist_dir is None:
             self.dist_dir = "dist"
diff --git a/Lib/packaging/command/bdist_dumb.py b/Lib/packaging/command/bdist_dumb.py
index f74b720..ed83c8e 100644
--- a/Lib/packaging/command/bdist_dumb.py
+++ b/Lib/packaging/command/bdist_dumb.py
@@ -13,6 +13,7 @@
 from packaging.errors import PackagingPlatformError
 from packaging import logger
 
+
 class bdist_dumb(Command):
 
     description = 'create a "dumb" built distribution'
@@ -23,7 +24,7 @@
                      "platform name to embed in generated filenames "
                      "(default: %s)" % get_platform()),
                     ('format=', 'f',
-                     "archive format to create (tar, ztar, gztar, zip)"),
+                     "archive format to create (tar, gztar, zip)"),
                     ('keep-temp', 'k',
                      "keep the pseudo-installation tree around after " +
                      "creating the distribution archive"),
@@ -44,10 +45,9 @@
 
     boolean_options = ['keep-temp', 'skip-build', 'relative']
 
-    default_format = { 'posix': 'gztar',
-                       'nt': 'zip',
-                       'os2': 'zip' }
-
+    default_format = {'posix': 'gztar',
+                      'nt': 'zip',
+                      'os2': 'zip'}
 
     def initialize_options(self):
         self.bdist_dir = None
@@ -69,8 +69,9 @@
             try:
                 self.format = self.default_format[os.name]
             except KeyError:
-                raise PackagingPlatformError(("don't know how to create dumb built distributions " +
-                       "on platform %s") % os.name)
+                raise PackagingPlatformError(
+                    "don't know how to create dumb built distributions "
+                    "on platform %s" % os.name)
 
         self.set_undefined_options('bdist', 'dist_dir', 'plat_name')