cros_sdk: Drop --unmount

This was associated with the --use-image feature, which we're dropping.

Leave the BAPI as a no-op.

BUG=b:266878468
TEST=./run_tests

Change-Id: If472a3d8d221ef8d3e0755c66acc7419282dad89
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4305423
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Brian Norris <briannorris@chromium.org>
Tested-by: Brian Norris <briannorris@chromium.org>
diff --git a/api/controller/sdk.py b/api/controller/sdk.py
index 945d61f..7dc489c 100644
--- a/api/controller/sdk.py
+++ b/api/controller/sdk.py
@@ -210,10 +210,9 @@
 
 @faux.all_empty
 @validate.validation_complete
-def Unmount(input_proto, _output_proto, _config):
+def Unmount(_input_proto, _output_proto, _config):
     """Unmount a chroot"""
-    chroot = controller_util.ParseChroot(input_proto.chroot)
-    sdk.Unmount(chroot)
+    # Deprecated. Do nothing.
 
 
 @faux.all_empty