DCD output has been removed

[danielhollas]

I've decided to remove the DCD trajectory output format because:

1. I am not sure it is working
2. Not sure if anybody needs it
3. it has portability issues (uses GNU-specific function that doesn't work with some compilers, see Don't include the main program in libfms.a #29)

That being said, if people need this, very happy to bring it back. Please comment on this issue if that is the case!