Merge pyodide_py into python_stdlib.zip. ### Description

Merges pyodide_py.tar into python_stdlib.zip. This reduces the number of network requests during the initialization.

The original intention of splitting pyodide_py.tar from pyodide.asm.data was to give users an option to provide custom files (#2023), which is now available by modifying python_stdlib.zip directly. So I think there is no reason to have both python_stdlib.zip and pyodide_py.tar.

### Checklists

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests

package:
  name: pkg_2
  version: 1.0.0
source:
  sha256: deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef
  url: https://dummy-url-that-not-exists.com/pkg_2.tar.gz
requirements:
  host:
    - pkg_3
  run:
    - pkg_3
test:
  imports:
    - pkg_2

package:
  name: pkg_2
  version: 1.0.0
source:
  sha256: deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef
  url: https://dummy-url-that-not-exists.com/pkg_2.tar.gz
requirements:
  host:
    - pkg_3
  run:
    - pkg_3
test:
  imports:
    - pkg_2
