FEM: let gmsh infer format from file name

I sometimes use the FEM workbench to create meshes for a problem that
I'll solve with an external FE solver that doesn't yet have workbench
integration, or to prepare a Gmsh file for tweaks from directly running
Gmsh. The .unv format is pretty limited on technical grounds so I rename
the file to .msh (can express everything Gmsh can) or a
parallel-friendly format. Explicitly setting Mesh.Format = 2 is
confusing because this line also needs to be fixed (or deleted) when
renaming the output file name.

src/Mod/Fem/femmesh/gmshtools.py

@@ -869,7 +869,6 @@ class GmshTools():
 
         # save mesh
         geo.write("// save\n")
-        geo.write("Mesh.Format = 2;\n")  # unv
         if self.group_elements and self.group_nodes_export:
             geo.write("// For each group save not only the elements but the nodes too.;\n")
             geo.write("Mesh.SaveGroupsOfNodes = 1;\n")

src/Mod/Fem/femtest/data/elmer/group_mesh.geo

@@ -41,7 +41,6 @@ Mesh  3;
 Coherence Mesh; // Remove duplicate vertices
 
 // save
-Mesh.Format = 2;
 // Ignore Physical definitions and save all elements;
 Mesh.SaveAll = 1;
 Save "/tmp/tmpjVhNNb.unv";