Unvendor pydoc_data and _pydecimal. ### Description

Removes / unvendors some python modules:

- Remove `_aix_support.py`, which is for supporting IBM AIX OS.

- Unvendor `_pydecimal.py`.
  - _pydecimal is a pure Python implementation of `decimal` module. [Importing `decimal` fallbacks](https://github.com/python/cpython/blob/main/Lib/decimal.py) to `_pydecimal` if the C-implementation `_decimal` is not available. In our case, _decimal is available, so _pydecimal will not be normally used. 

- Unvendor `pydoc_data`.
  - pydoc_data contains [a large (~700KB) dictionary](https://github.com/python/cpython/blob/main/Lib/pydoc_data/topics.py) for explaining python builtins. This is mostly used when `help("...")` is called.

### Checklists

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- [x] Add new / update outdated documentation

package:
  name: logbook
  version: 1.5.3
  top-level:
    - logbook
source:
  url: https://files.pythonhosted.org/packages/2f/d9/16ac346f7c0102835814cc9e5b684aaadea101560bb932a2403bd26b2320/Logbook-1.5.3.tar.gz
  sha256: 66f454ada0f56eae43066f604a222b09893f98c1adc18df169710761b8f32fe8

requirements:
  host:
    - distutils
    - setuptools

build:
  script: |
    python -c 'from Cython.Build.Cythonize import main; main(["./logbook/_speedups.pyx"])'

about:
  home: http://logbook.pocoo.org/
  PyPI: https://pypi.org/project/logbook
  summary: A logging replacement for Python
  license: BSD

package:
  name: logbook
  version: 1.5.3
  top-level:
    - logbook
source:
  url: https://files.pythonhosted.org/packages/2f/d9/16ac346f7c0102835814cc9e5b684aaadea101560bb932a2403bd26b2320/Logbook-1.5.3.tar.gz
  sha256: 66f454ada0f56eae43066f604a222b09893f98c1adc18df169710761b8f32fe8

requirements:
  host:
    - distutils
    - setuptools

build:
  script: |
    python -c 'from Cython.Build.Cythonize import main; main(["./logbook/_speedups.pyx"])'

about:
  home: http://logbook.pocoo.org/
  PyPI: https://pypi.org/project/logbook
  summary: A logging replacement for Python
  license: BSD
