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/btContactConstraint.h

@@ -30,7 +30,6 @@ protected:
 
 public:
 
-	btContactConstraint();
 
 	btContactConstraint(btPersistentManifold* contactManifold,btRigidBody& rbA,btRigidBody& rbB);