Revert "[mms] By default, use TLS if available and necessary to login to server."

This breaks logging in completely for me:

S: * OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE  XIMAPPROXY] neo Cyrus IMAP v2.4.16-Debian-2.4.16-4 server ready
C: 1 STARTTLS
S: 1 BAD Please login first
C: 2 STARTTLS
S: 2 BAD Please login first
C: 3 STARTTLS
S: 3 BAD Please login first
C: 4 STARTTLS
S: 4 BAD Please login first

This reverts commit 93421174c901ffbded46a35cc8e7ec3b60ea5769.