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- [x] Add new / update outdated documentation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: pytest-benchmark
  version: 4.0.0
  top-level:
    - pytest_benchmark
source:
  url: https://files.pythonhosted.org/packages/28/08/e6b0067efa9a1f2a1eb3043ecd8a0c48bfeb60d3255006dcc829d72d5da2/pytest-benchmark-4.0.0.tar.gz
  sha256: fb0785b83efe599a6a956361c0691ae1dbb5318018561af10f3e915caa0048d1
  patches:
    - patches/0001-Remove-cpuinfo.patch
about:
  home: https://github.com/ionelmc/pytest-benchmark
  PyPI: https://pypi.org/project/pytest-benchmark
  summary:
    A ``pytest`` fixture for benchmarking code. It will group the tests into
    rounds that are calibrated to the chosen timer.
  license: BSD-2-Clause

package:
  name: pytest-benchmark
  version: 4.0.0
  top-level:
    - pytest_benchmark
source:
  url: https://files.pythonhosted.org/packages/28/08/e6b0067efa9a1f2a1eb3043ecd8a0c48bfeb60d3255006dcc829d72d5da2/pytest-benchmark-4.0.0.tar.gz
  sha256: fb0785b83efe599a6a956361c0691ae1dbb5318018561af10f3e915caa0048d1
  patches:
    - patches/0001-Remove-cpuinfo.patch
about:
  home: https://github.com/ionelmc/pytest-benchmark
  PyPI: https://pypi.org/project/pytest-benchmark
  summary:
    A ``pytest`` fixture for benchmarking code. It will group the tests into
    rounds that are calibrated to the chosen timer.
  license: BSD-2-Clause
