Removes project_overview_reorg feature flag

What does this MR do and why?

Removes project_overview_reorg feature flag (#432034 (closed))

Removes old code and enables the changes from FF project_overview_reorg by default.

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Related to ✂️ UX Paper Cuts 16.10 → Groups & Projects (#424397 - closed), Project overview page reoganisation: add sidebar (!137025 - merged), #432034 (closed)+, Create sidebar to display project overview meta... (#431537 - closed)