KMail: don't sync after save, don't reload after last sync

Summary:

• save() takes care of sync() already, if anything changed.
• When quitting there's no reason to reload the configuration.

Test Plan: None yet

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: kde-pim

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D14509