Streamline macOS build variables on `conda_build_config.yaml`
This MR streamlines macOS build variables following recipe at https://conda-forge.org/docs/maintainer/knowledge_base.html#requiring-newer-macos-sdks
This MR streamlines macOS build variables following recipe at https://conda-forge.org/docs/maintainer/knowledge_base.html#requiring-newer-macos-sdks