Error importing `check_python_3` with new version of distributed

[kmpaul]

What happened:

When dask-mpi CLI is used, it attempts to import check_python_3 from distributed.cli.utils, which now fails because that function has been removed.

What you expected to happen:

We shouldn't need to check for Python 3 any more.

Minimal Complete Verifiable Example:

$ conda create -y --name test dask-mpi
$ dask-mpi --help
Traceback (most recent call last):
  File ".../envs/daskmpi/bin/dask-mpi", line 7, in <module>
    from dask_mpi.cli import go
  File ".../envs/daskmpi/lib/python3.10/site-packages/dask_mpi/cli.py", line 6, in <module>
    from distributed.cli.utils import check_python_3
ImportError: cannot import name 'check_python_3' from 'distributed.cli.utils' (.../envs/daskmpi/lib/python3.10/site-packages/distributed/cli/utils.py)

Anything else we need to know?:

I'm working on a PR to fix this now.

Environment:

• Dask version: 2022.4.0
• Python version: 3.10.4
• Operating System: MacOS
• Install method (conda, pip, source): conda