Mac: Don't register for Pan Gestures.

This will enable touch events for the viewport
widget, which has undesired side effects (see task).

Fixes a regression from Qt 4.

Task-number: QTBUG-38815
Change-Id: I7b9c0d1de985d1c82f946140fecf460fcfc5e686
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>