QNX: Use only one .7z file for Essentials and Addons

There is no need to split the binaries into qt5_essentials.7z and
qt5_addons.7z

This change makes the configuration of QNX installers easier from
a build perspective and from a packaging perspective.

This also allows us to (re)use the qt5_essentials.7z file from
builds made in other environments.

Change-Id: I876392cfac9237d785545867a22f730e532ffaac
Reviewed-by: Wolfgang Bremer <wbremer@blackberry.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>