tests(mimetreeparser): Tests that are have no depdenency against MessageViewer...

tests(mimetreeparser): Tests that are have no depdenency against MessageViewer should move to MimeTreeParser.

Summary: Simple move of tests to the right place

Reviewers: dvratil

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D23806