Changed the password $valid check condition

$user will always be an object and User::getPasswordValidity will
always return either true, a string or a (non-empty) array
combined with AND (&&), this will always be true"
Removed message 'config-admin-password-same' as it was used nowhere.

Bug: 41392
Change-Id: Idc2cb80ca4541d1120e18aad3261aece7bd72122
Merge "Changed the password $valid check condition"