Remove redundancy code
Remove redundancy code

When we pass secret_mode and kek_datum_model to
EndcryptedDatum [1], the __init__ function of
the class set secret_id attribute [2]. So no need
to have the line of code #346 [3]

[1] https://github.com/openstack/barbican/blob/master/barbican/plugin/store_crypto.py#L312
[2] https://github.com/openstack/barbican/blob/master/barbican/model/models.py#L457
[3] https://github.com/openstack/barbican/blob/master/barbican/plugin/store_crypto.py#L316

Change-Id: Ia419dccfc73aba88d4e00384a0a11926781bfeb3

openstack/barbican,openstack/barbican