Abilities API: Stop HTML-escaping the ability name in WP_Error messages

Ability names are pattern-validated at registration, so `esc_html()` on them is always a no-op. Drop it from the `WP_Error` messages, which are commonly serialized to JSON where the escaping would be incorrect.

Follow-up to [62398].
See #64311.



git-svn-id: https://develop.svn.wordpress.org/trunk@62401 602fd350-edb4-49c9-b593-d223f7449a82