db: Remove unnecessary timezone configuration
db: Remove unnecessary timezone configuration

The DateTime data type in SQLAlchemy defaults to non-timezone aware
timestamps [1]. There's no need to specify this. Removing it aligns our
model definition with the migration creating it.

[1] https://docs.sqlalchemy.org/en/14/core/type_basics.html#sqlalchemy.types.DateTime

Change-Id: I74e82c088015d2383c81b0951378058a4ba530c0
Signed-off-by: Stephen Finucane <4725dc7f3632bf126d9fbdc30c347e91e8d2fe16@redhat.com>

openstack/cinder,mahak/cinder,openstack/cinder,mahak/cinder