[FIX] survey: Do not parse datetime as date
[FIX] survey: Do not parse datetime as date

Commit 98d0424 (merged in saas-12.1) fixed a Deprecated warning by using
`field_utils.parse.date` instead of relying on
moment to parse the date.
However, a datetime question type was added in saas-12.2.
When the fix commit was forward ported, the parsing of datetime
broke as `field_utils.parse.date` can't parse a datetime.

Fix: use `field_utils.parse.datetime` if `questiontype === 'datetime'`.

Also, defining `toJSON` method is no longer necessary because
it is already done in the field_utils methods.
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo