cros_sdk: scrub dead tarball code

Cleanup logic that hasn't mattered in years:
* bzip2-vs-xz: We switched to XZ in 2012 for the SKD & bootstrap
* stage3-vs-sdk: We switched to self-bootstrap in 2019
* cros-sdk-overlays-*: We dropped this in ~2018

BUG=None
TEST=CQ passes

Change-Id: Ieef5292a9f714c1e4eab9ada0b5cf472073dd533
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3633292
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Lizzy Presland <zland@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Lizzy Presland <zland@google.com>
diff --git a/scripts/cros_sdk_unittest.py b/scripts/cros_sdk_unittest.py
index 6836014..85415e7 100644
--- a/scripts/cros_sdk_unittest.py
+++ b/scripts/cros_sdk_unittest.py
@@ -60,17 +60,16 @@
     """Basic test of GetArchStageTarballs."""
     self.assertCountEqual([
         'https://storage.googleapis.com/chromiumos-sdk/cros-sdk-123.tar.xz',
-        'https://storage.googleapis.com/chromiumos-sdk/cros-sdk-123.tbz2',
     ], cros_sdk.GetArchStageTarballs('123'))
 
   def testFetchRemoteTarballsEmpty(self):
     """Test FetchRemoteTarballs with no results."""
     m = self.PatchObject(retry_util, 'RunCurl')
     with self.assertRaises(ValueError):
-      cros_sdk.FetchRemoteTarballs(self.tempdir, [], 'tarball')
+      cros_sdk.FetchRemoteTarballs(self.tempdir, [])
     m.return_value = cros_build_lib.CommandResult(stdout=b'Foo: bar\n')
     with self.assertRaises(ValueError):
-      cros_sdk.FetchRemoteTarballs(self.tempdir, ['gs://x.tar'], 'tarball')
+      cros_sdk.FetchRemoteTarballs(self.tempdir, ['gs://x.tar'])
 
   def testFetchRemoteTarballsSuccess(self):
     """Test FetchRemoteTarballs with a successful download."""
@@ -82,7 +81,7 @@
     self.PatchObject(retry_util, 'RunCurl', return_value=curl)
     self.assertEqual(
         os.path.join(self.tempdir, 'tar'),
-        cros_sdk.FetchRemoteTarballs(self.tempdir, ['gs://x/tar'], 'tarball'))
+        cros_sdk.FetchRemoteTarballs(self.tempdir, ['gs://x/tar']))
 
 
 @unittest.skipIf(cros_build_lib.IsInsideChroot(),