[sumac] fix: hide library_v2 and itembank in legacy library page

[navinkarkera]

Hide options to add library_v2 and itembank blocks in legacy library page.

(cherry picked from commit 0f7eb29)

Backport of #35772

[openedx-webhooks]

Thanks for the pull request, @navinkarkera!

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[pomegranited]

👍 Works in sumac too, thank you @navinkarkera !

• I tested this on my tutor dev stack using the PR test instructions
• I read through the code
• I checked for accessibility issues N/A
• Includes documentation N/A
• User-facing strings are extracted for translation N/A