feat: remove legacy library content block from component templates

[salman2013]

Summary

• Removes the library template from the Studio add-component strip, preventing creation of new LegacyLibraryContentBlock instances via the UI
• Removes 'library' from COMPONENT_TYPES, its display name entry, the library block types loop, the component_not_supported_by_library list, and the libraries_v1_enabled() filter in _filter_disabled_blocks

Existing library_content blocks are fully unaffected:

• Randomized settings editor continues to work
• "View all" still navigates to the MFE-based children view
• Migration to v2 libraries still works

Companion frontend PR: openedx/frontend-app-authoring#3180

Ticket: #38058

Test plan

• Verify the "Legacy Library Content" button no longer appears in the add-component strip on a course unit
• Verify existing library_content blocks still render correctly
• Verify the randomized settings editor still works on existing legacy library content blocks
• Verify "View all" still navigates to the MFE-based children view
• Verify migration of legacy library content blocks to v2 still works

Testing Results

[openedx-webhooks]

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[kdmccormick]

The approach looks good! Can you also confirm that the legacy library block doesn't show up under "Advanced" ?

Please have someone else from Aximprovements review as well @salman2013 and then I'll approve and merge.