Removed Duplicate Message

[AlajeBash]

To remove the Duplicate Message Definition i combine the point.fb and point2d.fb file together and remove the duplicated namespace seerep.fb; line. Here's how the code look like:

namespace seerep.fb;

table Point2D {
  x: double;
  y: double;
}

table Point {
  x: double;
  y: double;
  z: double;
}

[jarkenau]

That's not really was #261 is about. Either the definition of the Point or Vector3 can be removed since they are essential the same. This additionally requires checking if other messages depend on it. I would tend to call the resulting message Point3D, since it's more consistent with Point2D. If you change the PR in that way we can merge it.