Fix T45080: Scale of exported .fbx is wrong in 2.75.

Man... this scaling issue becomes ridiculous!

Tried to fix it again also regarding (what is supposed to be) FBX scale/units handling.
Since we store Blender's unit system (with 1BU == 1m in case of none) as the UnitScaleFactor
element, we actually *do not* have to also scale objects themselves... In theory.

Since I have to wait hours here to get my UE4 repo updated and rebuild the monster,
comitting this now, we'll see later for FBXSDK behavior.