Removed empty constructors for constraints, I don't recall why we added them (possibly SPU) but if we really need them we have to revert this.

Moved static fixed body into a static function 'getFixedBody' to avoid issues when embedding Bullet in C#/CLI managed code.

src/BulletDynamics/ConstraintSolver/btHingeConstraint.h

@@ -98,7 +98,6 @@ public:
 
 	btHingeConstraint(btRigidBody& rbA,const btTransform& rbAFrame, bool useReferenceFrameA = false);
 
-	btHingeConstraint();
 
 	virtual void	buildJacobian();