Unassigns a user from any shortcut set they may have been assigned to.
The user will go back to using whatever default set applies.
$account: A user account that will be removed from the shortcut set assignment.
TRUE if the user was previously assigned to a shortcut set and has been successfully removed from it. FALSE if the user was already not assigned to any set.
function shortcut_set_unassign_user($account) {
$deleted = db_delete('shortcut_set_users')
->condition('uid', $account->uid)
->execute();
return (bool) $deleted;
}