Revert "Posteo: max TLS 1.2"

This reverts commit 5640f42fcd.

app/src/main/res/xml/providers.xml

@@ -402,7 +402,6 @@
         documentation="Please check if <a href="https://posteo.de/en/help/activating-additional-email-account-protection">additional email account protection</a> isn't enabled."
         domain="posteo\\..*"
         link="https://posteo.de/en/help/how-do-i-set-up-posteo-in-an-email-client-pop3-imap-and-smtp"
-        maxtls="1.2"
         user="*@posteo.net">
         <imap
             host="posteo.de"