Remove `useNewVideoUploadsPage` waffle flag (deferred from #3063)

[farhan]

🛑 Status: On hold — PR #3106 closed (not merged)

We are not removing this flag yet. The MFE-side read must follow the upstream feature decision openedx/edx-platform#37972, not lead it.

➡️ Full reasoning: closing comment below. Revisit once #37972 lands a decision.

Related stories (waffle-flag removal effort)

• Epic: Complete the MFE conversion process for frontend-app-authoring #3089 — Complete the MFE conversion process
• Remove Legacy UI Waffle Flags #3063 (Part 1) — Remove legacy routing waffle flags · PR Remove Legacy UI Waffle Flags [DEPR] #3069 (review comment that split this out)
• Deep dive into the usage/removal of feature waffle flags #3090 (Part 2) — Remove feature waffle flags
• This ticket (split out of Remove Legacy UI Waffle Flags #3063): useNewVideoUploadsPage

Summary

Remove the useNewVideoUploadsPage waffle flag from frontend-app-authoring. It was split out of #3063 / PR #3069 because — unlike the routing flags — it does not select between a legacy Django page and an MFE route; it gates a separate, edX/MIT-specific feature (backend flag contentstore.new_studio_mfe.use_new_video_uploads_page, default False, "off by default for the community").

[farhan]

Closing PR #3106 without merging — flag removal on hold

After reviewing the upstream state, we're keeping useNewVideoUploadsPage for now and closing PR #3106.

Why:

• refactor: Drop the unused legacy video upload page. openedx-platform#37582 (merged) dropped the legacy video uploads page but deliberately kept the contentstore.new_studio_mfe.use_new_video_uploads_page flag in place — to keep the new page flagged off for the community, since both the old and new pages only work on edx.org.
• Make the videos page community-friendly or deprecate it openedx-platform#37972 (open) is where the actual decision lives: make the videos page community-friendly, genericize it with plugin slots, or deprecate it. Two of those three outcomes would make the MFE removal the wrong change.

Removing the MFE-side read now would un-gate an edX/MIT-only feature for community installs (most visibly the VideoSettingsModal "Replace video" button rendering unconditionally). The MFE cleanup should follow the upstream decision, not lead it.

We'll revisit once #37972 lands a decision.

[feanil]

This makes sense to me. Improvements to the video page are not the focus of the current cleanup.

This work is blocked on openedx/openedx-platform#37972