Remove stretch from uprev script

We are dropping test support for stretch, as our users now have an
upgrade path.

BUG=chromium:1154444
TEST=none

Disallow-Recycled-Builds: test-failures
Change-Id: I4c2f6e4a5d5276d55f6a1d7e354d9b91efbd87a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/containers/cros-container-guest-tools/+/2570834
Reviewed-by: David Munro <davidmunro@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Fergus Dall <sidereal@google.com>
diff --git a/scripts/uprev.py b/scripts/uprev.py
index 2ab9e22..6c326cd 100755
--- a/scripts/uprev.py
+++ b/scripts/uprev.py
@@ -55,7 +55,7 @@
             file_arch = arch
 
         for ctype in ['test', 'app_test']:
-            for release in ['stretch', 'buster']:
+            for release in ['buster']:
                 base_url = f'gs://cros-containers-staging/{milestone}' \
                     f'/images/debian/{release}/{arch}/{ctype}/{latest_container}/'