Remove partition support from the Gmsh reader.
Remove partition support from the Gmsh reader.

This permits us to make a range of optimisations and
simplifications to the code.

tjcorona/PyFR,tjcorona/PyFR,Aerojspark/PyFR,BrianVermeire/PyFR,iyer-arvind/PyFR,tjcorona/PyFR