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- [x] Add new / update outdated documentation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: newick
  version: 1.4.0
  top-level:
    - newick
source:
  url: https://files.pythonhosted.org/packages/28/b5/8254e098b9f8d6dd2768451f26b38a0863a5410a319b16a7ace629c72f5e/newick-1.4.0-py2.py3-none-any.whl
  sha256: 5a44d12b3cacab1a4450a1af483b1d9542e854bd326e461b30ad8f72415e15e4
about:
  home: https://github.com/dlce-eva/python-newick
  PyPI: https://pypi.org/project/newick
  summary: A python module to read and write the Newick format
  license: Apache 2

package:
  name: newick
  version: 1.4.0
  top-level:
    - newick
source:
  url: https://files.pythonhosted.org/packages/28/b5/8254e098b9f8d6dd2768451f26b38a0863a5410a319b16a7ace629c72f5e/newick-1.4.0-py2.py3-none-any.whl
  sha256: 5a44d12b3cacab1a4450a1af483b1d9542e854bd326e461b30ad8f72415e15e4
about:
  home: https://github.com/dlce-eva/python-newick
  PyPI: https://pypi.org/project/newick
  summary: A python module to read and write the Newick format
  license: Apache 2
