Remove CS_DISABLE_DEPENDENCY_LIST from scan execution policies

What does this MR do and why?

The CS_DISABLE_DEPENDENCY_LIST env var is being removed in 17.0 since it is no longer useful: https://docs.gitlab.com/ee/update/deprecations.html?removal_milestone=17.0#dependency_files-is-deprecated

This MR removes that env var from the Security Policies constant.

See #439782 (closed)

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