remove requires-python from build-system table

[wheelsandmetal]

This key belongs in the project table which isn't defined.

https://packaging.python.org/en/latest/specifications/pyproject-toml/#declaring-project-metadata-the-project-table

Was running into

    - Installing qcore (1.10.1): Failed

  BuildSystemTableValidationError

  Failed to validate `build-system` in pyproject.toml: Unknown properties: requires-python

  at /opt/homebrew/Cellar/poetry/1.8.3_2/libexec/lib/python3.12/site-packages/build/_builder.py:113 in _parse_build_system_table
      109│
      110│     unknown_props = build_system_table.keys() - {'requires', 'build-backend', 'backend-path'}
      111│     if unknown_props:
      112│         msg = f'Unknown properties: {", ".join(unknown_props)}'
    → 113│         raise BuildSystemTableValidationError(msg)
      114│
      115│     return build_system_table
      116│
      117│

Cannot install qcore.

when installing pyanalyze with poetry.

[JelleZijlstra]

Thanks, could you move it to a new [project] table instead?