[etwist] remove no-longer-necessary uicache cleaning
It was done before we were actually up, which means it could be too
eager when combined with #6893185.
Closes #6893247.
change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')