chore: remove invalid license expression

[henryiii]

This is invalid according to PEP 621 (which causes validate-pyproject to fail, from repo-review). There's no need for it anyway, as the Trove classifiers are sufficient.

Repo-review output:

General

• Detected build backend: hatchling.build
• Detected license(s): BSD License

?	Name	Description
❌	PY004	Has docs folder Projects must have documentation in a folder called docs (disable if not applicable)

GitHub Actions

?	Name	Description
❌	GH102	Auto-cancel on repeated PRs At least one workflow should auto-cancel. concurrency: group: ${{ github.workflow }}-${{ github.ref }} cancel-in-progress: true

Pre-commit

?	Name	Description
❌	PC111	Uses blacken-docs Use https://github.com/adamchainz/blacken-docs instead of https://github.com/asottile/blacken-docs in .pre-commit-config.yaml

MyPy

?	Name	Description
❌	MY102	MyPy show error codes Must have show_error_codes = true. This will print helpful error codes for users that clarify why something fails if you need to skip it.
❌	MY103	MyPy warn unreachable Must have warn_unreachable = true to pass this check. There are occasionally false positives (often due to platform or Python version static checks), so it's okay to ignore this check. But try it first - it can catch real bugs too.
❌	MY104	MyPy enables ignore-without-code Must have "ignore-without-code" in enable_error_code = [...]. This will force all skips in your project to include the error code, which makes them more readable, and avoids skipping something unintended.
❌	MY105	MyPy enables redundant-expr Must have "redundant-expr" in enable_error_code = [...]. This helps catch useless lines of code, like checking the same condition twice.
❌	MY106	MyPy enables truthy-bool Must have "truthy-bool" in enable_error_code = []. This catches mistakes in using a value as truthy if it cannot be falsey.

Documentation

?	Name	Description
❌	RTD100	Uses ReadTheDocs (pyproject config) Should have a .readthedocs.yaml file in the root of the repository. Modern ReadTheDocs requires (or will require soon) this file.

Validate-PyProject

Checks [build-system], [project], [tool.repo-review], [tool.setuptools]

?	Name	Description
❌	VPP001	Validate pyproject.toml Invalid pyproject.toml! Error: project.license must be valid exactly by one definition (2 matches found): - keys: 'file': {type: string} required: ['file'] - keys: 'text': {type: string} required: ['text']