[FIX] google_calendar: do not copy user Google info

If a user syncs his calendar with Google,
and a second user is created in the database by copying this first
user, the Google information of the first user was copied
(The Google account to sync, the token to use, the last
syncrhonization date, ...), which is obviously wrong.

On calendar syncrhonization, which can be done
manually or automatically with the according cron, all
events of the first user were created a second time,
as a second user synchronized the same Google Calendar.

opw-674141