Simplify the `jupyter kernelspec` setup

[davidorme]

Description

This removes the ve_python3 specific kernel for jupyter and falls back to poetry run/shell setting the jupyter kernelspec to point to the active poetry venv for the project.

The tests below and RTD all work, showing this simplification works as expected: https://virtual-ecosystem.readthedocs.io/en/427-simplify-the-jupyter-kernelspec-setup/

Closes #427

Type of change

• [ ] New feature (non-breaking change which adds functionality)
• [ ] Optimization (back-end change that speeds up the code)
• [ ] Bug fix (non-breaking change which fixes an issue)

Key checklist

• [ ] Make sure you've run the pre-commit checks: $ pre-commit run -a
• [ ] All tests pass: $ poetry run pytest

Further checks

• [ ] Code is commented, particularly in hard-to-understand areas
• [ ] Tests added that prove fix is effective or that feature works

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.60%. Comparing base (0ccb1c7) to head (73686c6).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #429 +/- ## ======================================== Coverage 94.60% 94.60% ======================================== Files 70 70 Lines 3744 3744 ======================================== Hits 3542 3542 Misses 202 202 ```

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