adding breaking change warning to az sig image-version create/update

Author: Naga Nandyala

src/azure-cli/azure/cli/command_modules/vm/_breaking_change.py

@@ -2,7 +2,7 @@
 # Copyright (c) Microsoft Corporation. All rights reserved.
 # Licensed under the MIT License. See License.txt in the project root for license information.
 # --------------------------------------------------------------------------------------------
-from azure.cli.core.breaking_change import register_default_value_breaking_change, register_other_breaking_change
+from azure.cli.core.breaking_change import register_default_value_breaking_change
 
 register_default_value_breaking_change(command_name='vm create',
                                        arg='--size',