build: do not generate setup.py by default

This is the first step in removing setup file generation from Poetry
projects. With this change, projects that require a setup.py to be
generated when a build script is used needs to explicitly set
`tool.poetry.build.generate-setup-file`, introduced in #26, to `true`
in `pyproject.toml`.

src/poetry/core/json/schemas/poetry-schema.json

@@ -666,7 +666,7 @@
  "generate-setup-file": {
  "type": "boolean",
  "description": "Generate and include a setup.py file in sdist.",
- "default": true
+ "default": false
  },
  "script": {
  "$ref": "#/definitions/build-script"

src/poetry/core/packages/project_package.py

@@ -72,4 +72,4 @@ def urls(self) -> dict[str, Any]:
  return urls
 
  def build_should_generate_setup(self) -> bool:
- return self.build_config.get("generate-setup-file", True)
+ return self.build_config.get("generate-setup-file", False)