Fix missing sys import in destroy-module firewall script

[Copilot]

The destroy-module/20firewall script references sys.stderr without importing the sys module, causing a NameError at runtime when firewall rule removal fails.

Changes

• Added import sys to imageroot/actions/destroy-module/20firewall

import os
import sys  # Added - required for sys.stderr usage on line 38
import agent

The script writes warnings to stderr when rich rule removal fails, but the import was missing from the initial implementation.

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