Do not add Type::Document/Presentation/Spreadsheet twice for MS Office docs

Summary:
The mimetype is matched with "powerpoint" and "excel" already, no need
to add it to the list a second time.
This has no influence on DB contents, as adding a term is idempotent, but
makes the QHash here and the returned QVector<Type> slightly smaller.

Reviewers: Baloo, Frameworks, ngraham, poboiko, lbeltrame

Reviewed By: lbeltrame

Subscribers: lbeltrame, kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D17089