Remove the old concretizer (#45215)

The old concretizer is still used to bootstrap clingo from source. If we switch to a DAG model
where compilers are treated as nodes, we need to either:

1. fix the old concretizer to support this (which is a lot of work and possibly research), or
2. bootstrap `clingo` without the old concretizer.

This PR takes the second approach and gets rid of the old concretizer code. To bootstrap
`clingo`, we store some concrete spec prototypes as JSON, select one according to the
coarse-grained system architecture, and tweak them according to the current host.

The old concretizer and related dead code are removed.  In particular, this removes
`Spec.normalize()` and related methods, which were used in many unit-tests to set
up the test context. The tests have been updated not to use `normalize()`.

- [x] Bootstrap clingo concretization based on a JSON file
- [x] Bootstrap clingo *before* patchelf
- [x] Remove any use of the old concretizer, including:
      * Remove only_clingo and only_original fixtures
      * Remove _old_concretize and _new_concretize
      * Remove _concretize_together_old
      * Remove _concretize_together_new
      * Remove any use of `SPACK_TEST_SOLVER`
      * Simplify CI jobs
- [x] ensure bootstrapping `clingo` works on on Darwin and Windows
- [x] Raise an intelligible error when a compiler is missing
- [x] Ensure bootstrapping works on FreeBSD
- [x] remove normalize and related methods

Signed-off-by: Todd Gamblin <tgamblin@llnl.gov>

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