concretizer: remove clingo command-line driver (#20362)

I was keeping the old `clingo` driver code around in case we had to run
using the command line tool instad of through the Python interface.

So far, the command line is faster than running through Python, but I'm
working on fixing that.  I found that if I do this:

```python
control = clingo.Control()
control.load("concretize.lp")
control.load("hdf5.lp")       # code from spack solve --show asp hdf5
control.load("display.lp")

control.ground([("base", [])])
control.solve(...)
```

It's just as fast as the command line tool. So we can always generate the
code and load it manually if we need to -- we don't need two drivers for
clingo. Given that the python interface is also the only way to get unsat
cores, I think we pretty much have to use it.

So, I'm removing the old command line driver and other unused code. We
can dig it up again from the history if it is needed.

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