Re #6564. Remove items applicable to older OS X.

i.e. versions that we no longer support.
Re #6563. Remove installer preflight script.

It was just cleaning up long-gone items so I don't think we
need it anymore. It can't be used with a DragNDrop installer anyway.
Re #6563. Switch to drag and drop install kit.

Replacing PackageMaker.
Re #6563. DragNDrop generator need plain text license only

It can't do anything with the rich text files.
Merge branch 'feature/6563_osx_dragndrop_installer' into develop