STYLE: Remove old cmake < 2.8.4 specific code

We are requiring at least cmake 2.8.6

Change-Id: Ia34c77bdfa866c4eba58f1b3f28d454e095a8851
Merge topic 'RemoveCmake2.8.4Code'

a43271f9 STYLE: Remove old cmake < 2.8.4 specific code