Block Editor: Remove a deprecated notice being generated by the meta box compat functions.

Props pento.

Merges [44248] into trunk.

Fixes #45456.
Built from https://develop.svn.wordpress.org/trunk@44315


git-svn-id: https://core.svn.wordpress.org/trunk@44145 1a063a9b-81f0-0310-95a4-ce76da25c4cd