remove unused 'joblib' and 'numba' dependencies, other packaging cleanup

[jameslamb]

Proposes some cleanup of packaging details, noticed while I was working on #2531

• removes runtime dependencies on joblib and numba for raft-dask
  • raft-dask doesn't directly import from these libraries, and the git blame didn't suggest any other reason that they were being pinned here
  • *checked with git grep -E 'joblib|numba'
• removes setup.cfg files
  • these are currently being ignored by tools, in favor of identical configuration in pyproject.toml and .flake8 files
  • e.g.

    raft/.pre-commit-config.yaml

    Lines 16 to 19 in bfd1906

    	- id: black
    	files: python/.*
    	# Explicitly specify the pyproject.toml at the repo root, not per-project.
    	args: ["--config", "pyproject.toml"]

• packages license files in conda packages
  • think these were just missed in the round of PRs like this: Add license file to conda packages cuml#6061
• removes some outdated / inaccurate comments in packaging configs

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[jameslamb]

/ok to test