Fix PV type in converter

There is a bug in the PV converter. It leads to setting the wrong PV type which confuses LoKi cuts later.

More description can be found here: Closes Moore#85 (closed)

enum RecVertexType {
  Unknown = 0,
  Vertex2D,
  Vertex3D,
  V0,
  Primary = LHCb::VertexBase::VertexType::Primary,
  LastRec = 10000
};

The problem is that Primary is not 4 but defined 100 in VertexBase. While it becomes 4 when casting from the enum in v2::RecVertex.

The converter is not meant to convert anything but primary vertices so it is fine to hard-wire the type here.