Chore: Remove invalid @throws WP_Error from register_block_*() doc-blocks

[justlevine]

Trac ticket: https://core.trac.wordpress.org/ticket/52217

This PR removes invalid @throws WP_Error annotations from the doc-blocks of the following functions:

• register_block_core_home_link()
• register_block_core_navigation_link()
• register_block_core_navigation_submenu()

These annotations are invalid for a few reasons:

• WP_Error is returnable, not Throwable
• WP_Error is not returned.
• A review of the functions' internals and render_callbacks doesn't show any attempts to either return a WP_Error or throw anything else.
  ( It's possible I missed something, but I'm pretty confident, as these are the only register_() functions in blocks/ that have any @throws annotation )

While this issue was surfaced via PHPStan in #7619 (trac: https://core.trac.wordpress.org/ticket/61175 ), it can be remediated independently of that ticket.

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