Remove duplicate MimeType entry in the desktop file

Summary: The duplicate MimeType entry causes issue for Fedora packaging because the desktop file is checked for conformity during this process. It fails because of the duplicate entry.

Reviewers: Elisa, mgallien

Reviewed By: Elisa, mgallien

Subscribers: mgallien, Elisa

Tags: Elisa

Differential Revision: https://phabricator.kde.org/D10241