Function delete_doc_format 

pub async fn delete_doc_format(
    __arg0: State<App>,
    tn_id: TnId,
    __arg2: Auth,
    __arg3: IdTag,
    __arg4: OptionalRequestId,
    __arg5: Path<String>,
) -> ClResult<(StatusCode, Json<ApiResponse<()>>)>

DELETE /api/doc-formats/{content_type} — drop the tenant’s row.

With a bundled entry behind it this is a revert, not a removal: the format resolves back to what the build ships. A content type the bundle also declares therefore cannot be turned off, only overridden — see cloudillo_core::bundled_apps.