Remove old and add new deprecations

[hakonanes]

Description of the change

• Remove kikuchipy.projections.ebsd_projections module
• Deprecate entire kikuchipy.projections module, as it is unused internally. If you depend on this module, please raise an issue here on GitHub.

Progress of the PR

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

Minimal example of the bug fix or new feature

>>> from orix.vector import Vector3d
>>> import kikuchipy as kp
>>> kp.projections.GnomonicProjection().vector2xy(Vector3d([0.5, 0, 0]))
/home/hakon/kode/kikuchipy/kikuchipy/projections/gnomonic_projection.py:40: VisibleDeprecationWarning: Function `vector2xy()` is deprecated and will be removed in version 0.9.0.
  @deprecated(since="0.8.0", removal="0.9.0")
array([[1.63312394e+16, 0.00000000e+00]])

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.