Update documentation to remove outdated function reference for display

[Alina-chan]

Description

This PR removes an outdated reference to a non-existent set_owned function in the Display module documentation. The reference caused confusion as the function is not present or used in the current code. The documentation has been updated to reference the correct public functions, such as add and add_multiple, which handle field additions in the Display object.

No functional changes have been made to the code; the update is purely a documentation fix.

Test plan

No tests were required.

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Release notes

This change does not impact any of the following components:

• [ ] Protocol:
• [ ] Nodes (Validators and Full nodes):
• [ ] Indexer:
• [ ] JSON-RPC:
• [ ] GraphQL:
• [ ] CLI:
• [ ] Rust SDK:
• [ ] REST API: