* Remove CI jobs related to Python 2.7
* Remove Python 2.7 specific code from Spack core
* Remove externals for Python 2 only
* Remove llnl.util.compat
Add a `project` block to the toml config along with development and CI
dependencies and a minimal `build-system` block, doing basically
nothing, so that spack can be bootstrapped to a full development
environment with:
```shell
$ hatch -e dev shell
```
or for a minimal environment without hatch:
```shell
$ python3 -m venv venv
$ source venv/bin/activate
$ python3 -m pip install --upgrade pip
$ python3 -m pip install -e '.[dev]'
```
This means we can re-use the requirements list throughout the workflow
yaml files and otherwise maintain this list in *one place* rather than
several disparate ones. We may be stuck with a couple more temporarily
to continue supporting python2.7, but aside from that it's less places
to get out of sync and a couple new bootstrap options.
Co-authored-by: Adam J. Stewart <ajstewart426@gmail.com>
