Remove new pipelines table feature flag [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Removes new_pipelines_table feature flag and cleans up instances of it's use in the codebase. This flag was used to port over the pipelines table to utilize GlTable. See more in the rollout issue.

The table is located at CI/CD > Pipelines, as well as on commits (pipelines tab) and merge requests (pipelines tab).

Related to (rollout issue): #322599 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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• Documentation (if required)
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• Style guides
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• 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

Security

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• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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