[FIX] l10n_fr_pos_cert: datetime.timedelta

When a user was closing a POS to go into the backend, and click on "Reprendre",
there was an error which prevent him to reopen the POS.

There was a confusion between object <datetime> and <datetime.datetime>, as
the previous code was trying to use the function timedelta() from datetime.datetime
instead of datetime. As a result, the error states that datetime.datetime has no
function timedelta.

opw-801523

addons/l10n_fr_pos_cert/models/pos.py

@@ -1,4 +1,4 @@
-from datetime import datetime
+from datetime import datetime, timedelta
 from hashlib import sha256
 from json import dumps
 import pytz
@@ -41,7 +41,7 @@ class pos_session(models.Model):
         self.ensure_one()
         date_today = datetime.utcnow()
         session_start = Datetime.from_string(self.start_at)
-        if not date_today - datetime.timedelta(hours=24) <= session_start:
+        if not date_today - timedelta(hours=24) <= session_start:
             raise UserError(_("This session has been opened another day. To comply with the French law, you should close sessions on a daily basis. Please close session %s and open a new one.") % self.name)
         return True