Minor optimizations for saving user personal information

* Remove double hook: the OC_User::changeUser triggers an
OC\AccountManager::userUpdated and the app is already listening to this
signal in its Application definition

* Make createCard not check if an card exists if we already checked
  previously. We also don't try to get the card if the user is disabled
  as we don't use the card in this case

We this change we go from 100 DB requests to 80 DB requests when saving
an user email address.

Signed-off-by: Carl Schwan <carl@carlschwan.eu>
(cherry picked from commit c6fd482edf33214a9ad4787e4cac278f871fa7c8)