lammps_dummy task not exists

I got an error when I ran
```
fab localhost lammps_dummy:lammps_dummy,cores=1
```
when I checked the [FabMD.py](https://github.com/UCL-CCS/FabMD/blob/master/FabMD.py) , I could not find the `lammps_dummy` task, and also in [config_files](https://github.com/UCL-CCS/FabMD/tree/master/config_files), there is no `lammps_dummy` folder

