Remove redundant `QueryLimiting.enable_whitelist?` method

What does this MR do?

The .enable? and .enable_whitelist? methods were originally logically different cca61980 but converged in 04b64288.

This MR removes .enable_whitelist?.

Note, a downstream MR !55717 (merged) will rename .whitelist as its a misused term that is offensive.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • [-] I have included a changelog entry.
  • I have not included a changelog entry because ~"technical debt".
• [-] Documentation (if required)
• Code review guidelines
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• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done