This reverts commit f17c7be.

…50851)

This reverts commit f17c7be.

Reverts #49589

There are, unfortunately, races in the cleanup code. We are seeing issues like this in CI:

```
        for bucket in self.cache_buckets():
            with self._fc.read_transaction(bucket) as f:
                if not f:
>                   raise RuntimeError(
                        "Attempting to clean non existent cache bucket" f" {bucket.name}"
                    )
E                   RuntimeError: Attempting to clean non existent cache bucket nc

lib/spack/spack/solver/asp.py:660: RuntimeError
```

and, more frequently:

```
self = PosixPath('/Users/runner/.local/state/spack/tv6pwnm/misc-cache/concretization/hy/hyrtccditoupfm3s64poficxh5cisl6d')

    def stat(self, *, follow_symlinks=True):
        """
        Return the result of the stat() system call on this path, like
        os.stat() does.
        """
>       return os.stat(self, follow_symlinks=follow_symlinks)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E       FileNotFoundError: [Errno 2] No such file or directory: '/Users/runner/.local/state/spack/tv6pwnm/misc-cache/concretization/hy/hyrtccditoupfm3s64poficxh5cisl6d'
```

The second issue appears to be that this sort:

```
        rm_reg.sort(key=lambda x: x.stat().st_mtime, reverse=True)
```

is calling stat() redundantly on entries while not holding any read lock on them. I suspect the first is also a race on bucket creation and deletion.

We can work this out later and merge for 1.1.