Remove all uses of runtime_hash; document lockfile formats and fix tests

This removes all but one usage of runtime hash. The runtime hash was being used to write
historical lockfiles for tests, but we don't need it for that; we can just save those
lockfiles.

- [x] add legacy lockfiles for v1, v2, v3
- [x] fix bugs with v1 lockfile tests (the dummy lockfile we were writing was not actually
      a v1 lockfile because it used the new spec file format).
- [x] remove all but one runtime_hash usage -- that one needs a small rework of the
      concretizer to really fix, as it's about separate concretization of build
      dependencies.
- [x] Document the history of the lockfile format in `environment/__init__.py`

share/spack/spack-completion.bash

@@ -1678,7 +1678,7 @@ _spack_solve() {
 _spack_spec() {
     if $list_options
     then
-        SPACK_COMPREPLY="-h --help -l --long -L --very-long -I --install-status -y --yaml -j --json --format -c --cover -N --namespaces --hash-type -t --types -U --fresh --reuse"
+        SPACK_COMPREPLY="-h --help -l --long -L --very-long -I --install-status -y --yaml -j --json --format -c --cover -N --namespaces -t --types -U --fresh --reuse"
     else
         _all_packages
     fi