Updates example to use current code

[davejtoews]

Description

checkHistoricalPasswords() no longer exists as a method but it was still present in the example code at the top of the file.

Manual testing steps

No code has been changed other than comments.

Issues

• Example code in Security/PasswordValidator uses method that no longer exists. #11572

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• This change is covered with tests (or tests aren't necessary for this change)
• Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• CI is green

[GuySartorelli]

Thanks!