fix remove physical group without geo internals
Loading a ".msh" then removing physical group from the API fails.
gmsh.open("mesh.msh")
groups = gmsh.model.get_physical_group(1)
gmsh.model.remove_physical_groups(groups)
Gmsh complains that the groups do not exist.
I tried adding a gmsh.model.geo.synchronize()
without success.
This commit fix my use case but the call to GEO_Internals should probably be avoided completely in this case.
I'm not sure if the return value should be true (success) or false (model not modified).