ENH: remove blocking communication for gather patterns

ENH: eliminate unnecessary duplicate communicator

- in globalMeshData previously had a comm_dup hack to avoid clashes
  with deltaCoeffs calculations. However, this was largely due to a
  manual implementation of reduce() that used point-to-point
  communication. This has since been updated to use an MPI_Allreduce
  and now an MPI_Allgather, neither of which need this hack.