Cleanup old abuse reports list implementation

What does this MR do and why?

Completes cleanup part of [Feature flag] Enable abuse_reports_list (#402613 - closed)

This MR removes code for the old and unused implementation of abuse reports list. The new implementation has been enabled globally in production 4 months ago without issues.

Screenshots or screen recordings

Old implementation (removed in this MR)	New implementation

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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