Removed PSA_ERROR_DOES_NOT_EXIST from psa_export_key
If the key doesn't exist by the time this call is made
then the handle is invalid,
which means that PSA_ERROR_INVALID_HANDLE should be
returned rather than "does not exist"
@@ -604,7 +604,6 @@ psa_status_t psa_destroy_key(psa_key_handle_t handle);
*
* \retval #PSA_SUCCESS
* \retval #PSA_ERROR_INVALID_HANDLE
- * \retval #PSA_ERROR_DOES_NOT_EXIST
* \retval #PSA_ERROR_NOT_PERMITTED
* The key does not have the #PSA_KEY_USAGE_EXPORT flag.
* \retval #PSA_ERROR_NOT_SUPPORTED
