[Tests] Silenced all deprecations in tests for 2.3

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

Also removed src/Symfony/Component/Security/Core/Tests/Validator/Constraints/UserPasswordValidatorTest.php as it was not running at all.

looks like this is a legacy file that missed a cleanup (test is never run if I'm not wrong?)