Checkmk Werk 13269: check_mail_loop: AssertionError when using PasswordStore

ID: 13269 Title: check_mail_loop: AssertionError when using PasswordStore Component: Checks & agents Level: 1 Class: Bug fix Version: 2.1.0p28 A leftover Python `assert` statement dealing with plaintext passwords only led to fatal AssertionError when using PasswordStore instead of plaintext passwords. This change simply removes those statements as already done on newer branches.