Undo CTE fix for PG11 [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This removes the PG 11 CTE estimator hacks. The feature flags were already disabled on production since 14.0.

Related issue: #326813 (closed)

Note: these feature flags were never on by default, we only enabled them on GL.com

Does this MR meet the acceptance criteria?

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