KSMTP: remove dependency on KMime, by removing setMessage().
Summary:
Update API DOX and unittest to use setData(QByteArray).
In practice, kmailtransport/plugins/smtp is already using that directly.
Test Plan: Compiles, unittest passes, all of kde/pim still compiles.
Reviewers: dvratil, vkrause
Subscribers: KDE PIM
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D12432