Remove custom scan action from Scan execution policy schema

Imam Hossainrequested to merge
477787-remove-custom-scan-action-from-scan-execution-policy-schema into master

What does this MR do and why?

This MR removes the custom scan action from the policy schema. The processing was removed in !159607 (merged) and it was removed from the UI in !160053 (merged).

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Related to #477787 (closed)

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