scripts: cros_sdk: deprecate --use-image

Start making people aware of our intention to remove this functionality.

BUG=b:266878468
TEST=CQ passes

Change-Id: I203701c16ee55de094e633ddb3fd2bcc8f731a29
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4199756
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_sdk.py b/scripts/cros_sdk.py
index 307e900..47c076a 100644
--- a/scripts/cros_sdk.py
+++ b/scripts/cros_sdk.py
@@ -71,7 +71,7 @@
 # Tools needed for --proxy-sim only.
 PROXY_NEEDED_TOOLS = ("ip",)
 
-# Tools needed when use_image is true (the default).
+# Tools needed when use_image is true.
 IMAGE_NEEDED_TOOLS = (
     "losetup",
     "lvchange",
@@ -1195,6 +1195,10 @@
             cros_build_lib.Die(
                 "Snapshot operations are not compatible with " "--nouse-image."
             )
+    if options.use_image:
+        logging.warning("--use-image is deprecated and will be removed soon.")
+        logging.warning("Please migrate, or create a new one with --delete.")
+        logging.warning("See http://b/266878468 for details.")
 
     # Discern if we need to create the chroot.
     if (