An early draft of the PSA crypto specification required multipart
operations to keep working after destroying the key. This is no longer
the case: instead, now, operations are guaranteed to fail. Mbed TLS
does not comply yet, and still allows the operation to keep going.
Stop testing Mbed TLS's non-compliant behavior.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>