remove runtime dependency on setuptools

[Ravencentric]

I skimmed the repo and could not find setuptools actually being used at runtime yet users get setuptools when they install ctranslate2. Note that you don't need a runtime dependency on setuptools to build a package with setuptools, pyproject.toml already includes setuptools as a build time dependency

❯ "ctranslate2" | uv pip compile -
Resolved 4 packages in 5ms
# This file was autogenerated by uv via the following command:
#    uv pip compile -
ctranslate2==4.8.1
numpy==2.5.2
    # via ctranslate2
pyyaml==6.0.3
    # via ctranslate2
setuptools==84.0.0
    # via ctranslate2

[jordimas]

Good catch, thanks!"