Remove deprecated generators and projections modules

[hakonanes]

Description of the change

This PR removes the deprecated generators and projections modules from develop in anticipation of a 0.9.0 release (which won't be for some time, I think).

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the unreleased
  section in CHANGELOG.rst.
• New contributors are added to release.py, .zenodo.json and
  .all-contributorsrc with the table regenerated.