Abilities: Strip internal schema keywords from abilities REST responses.

Remove WordPress-internal properties (`sanitize_callback`, `validate_callback`, `arg_options`) from ability `input_schema` and `output_schema` fields in REST responses. These properties are used server-side but are not valid JSON Schema keywords and cause client-side validators to fail.

Props jorgefilipecosta, ocean90, gziolo.
Fixes #65035.

git-svn-id: https://develop.svn.wordpress.org/trunk@62221 602fd350-edb4-49c9-b593-d223f7449a82