QPdfEngine - Remove Producer copyright notice

Remove the copyright notice from the PDF Producer field which could be
misunderstood. Comparison to other PDF Producers shows no other company
does this.

Based on https://codereview.qt-project.org/#change,70182

Task-number: QTBUG-33853
Change-Id: I3a2820c1466963e7391b4a9a729c7261a3582e0b
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: John Layt <jlayt@kde.org>