[Refactor] Slash-n-Burn Video BuiltIn XBlock

[farhan]

See parent story for initial details.

• We will also delete these html pages used in Built-In Video Block code.
• They exist in the extracted video block as well.

Relevant PR: openedx/openedx-platform#38466

Acceptance Criteria:

1. All functionalities of extracted Video Block should working fine
2. Video Editor of Studio and Content Library should working fine
3. All legacy methods inside Extracted Video Editor should be removed as well [or create story for them]