Remove docs update for SAST cleanup migration

What does this MR do and why?

This MR removes the docs changes made by Docs: Describe 17.3 one-time SAST cleanup migra... (!158872 - merged) • Adam Cohen, Connor Gilbert+ • 17.3 because of a bug which has prevented the migration from working correctly in %17.3. The bug has now been fixed, but since it's too late to get the bugfix added to %17.3, I'm removing the docs, and will re-add them targeting either %17.3.1 or %17.4.

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Related to #444926 (closed)