Allowing the client to delete revisions breaks the "audit trail" functionality. This is not allowed in WordPress and shouldn't be allowed through the API.
While not recommended, a plugin may opt-in to the previous behavior by setting a custom 'delete_post' capability for the revisions post type.
Props dlh, danielbachhuber, TimothyBlynJacobs, azaozz, kadamwhite.
Fixes#43709.
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