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- [x] Add new / update outdated documentation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: scikit-learn
  version: 1.2.0
  tag:
    - min-scipy-stack
  top-level:
    - sklearn
source:
  url: https://files.pythonhosted.org/packages/27/a0/95eae31ceabeb7710a694367816edfcc0ccb001c794c14b3b234c148ae50/scikit-learn-1.2.0.tar.gz
  sha256: 680b65b3caee469541385d2ca5b03ff70408f6c618c583948312f0d2125df680

build:
  cflags: -Wno-implicit-function-declaration

requirements:
  host:
    - numpy
    - scipy
  run:
    - scipy
    - joblib
    - threadpoolctl

test:
  imports:
    - sklearn
    - sklearn.calibration
    - sklearn.cluster
    - sklearn.compose
    - sklearn.covariance
    - sklearn.cross_decomposition
    - sklearn.datasets
    - sklearn.decomposition
    - sklearn.discriminant_analysis
    - sklearn.dummy
    - sklearn.ensemble
    - sklearn.exceptions
    - sklearn.externals
    - sklearn.feature_extraction
    - sklearn.feature_selection
    - sklearn.gaussian_process
    - sklearn.impute
    - sklearn.isotonic
    - sklearn.kernel_approximation
    - sklearn.kernel_ridge
    - sklearn.linear_model
    - sklearn.manifold
    - sklearn.metrics
    - sklearn.mixture
    - sklearn.model_selection
    - sklearn.multiclass
    - sklearn.multioutput
    - sklearn.naive_bayes
    - sklearn.neighbors
    - sklearn.neural_network
    - sklearn.pipeline
    - sklearn.preprocessing
    - sklearn.random_projection
    - sklearn.semi_supervised
    - sklearn.svm
    - sklearn.tree
    - sklearn.utils
about:
  home: http://scikit-learn.org
  PyPI: https://pypi.org/project/scikit-learn
  summary: A set of python modules for machine learning and data mining
  license: new BSD

package:
  name: scikit-learn
  version: 1.2.0
  tag:
    - min-scipy-stack
  top-level:
    - sklearn
source:
  url: https://files.pythonhosted.org/packages/27/a0/95eae31ceabeb7710a694367816edfcc0ccb001c794c14b3b234c148ae50/scikit-learn-1.2.0.tar.gz
  sha256: 680b65b3caee469541385d2ca5b03ff70408f6c618c583948312f0d2125df680

build:
  cflags: -Wno-implicit-function-declaration

requirements:
  host:
    - numpy
    - scipy
  run:
    - scipy
    - joblib
    - threadpoolctl

test:
  imports:
    - sklearn
    - sklearn.calibration
    - sklearn.cluster
    - sklearn.compose
    - sklearn.covariance
    - sklearn.cross_decomposition
    - sklearn.datasets
    - sklearn.decomposition
    - sklearn.discriminant_analysis
    - sklearn.dummy
    - sklearn.ensemble
    - sklearn.exceptions
    - sklearn.externals
    - sklearn.feature_extraction
    - sklearn.feature_selection
    - sklearn.gaussian_process
    - sklearn.impute
    - sklearn.isotonic
    - sklearn.kernel_approximation
    - sklearn.kernel_ridge
    - sklearn.linear_model
    - sklearn.manifold
    - sklearn.metrics
    - sklearn.mixture
    - sklearn.model_selection
    - sklearn.multiclass
    - sklearn.multioutput
    - sklearn.naive_bayes
    - sklearn.neighbors
    - sklearn.neural_network
    - sklearn.pipeline
    - sklearn.preprocessing
    - sklearn.random_projection
    - sklearn.semi_supervised
    - sklearn.svm
    - sklearn.tree
    - sklearn.utils
about:
  home: http://scikit-learn.org
  PyPI: https://pypi.org/project/scikit-learn
  summary: A set of python modules for machine learning and data mining
  license: new BSD
