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- [x] Add new / update outdated documentation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: pyproj
  version: 3.4.1
  top-level:
    - pyproj
source:
  url: https://files.pythonhosted.org/packages/c0/fc/fd53e45d2ad5862d32ab8614e70c3c1f52a8e0d8bd243ee6a23b6a481b4a/pyproj-3.4.1.tar.gz
  sha256: 261eb29b1d55b1eb7f336127344d9b31284d950a9446d1e0d1c2411f7dd8e3ac

requirements:
  host:
    - libproj
  run:
    - certifi
    - sqlite3

build:
  script: |
    export PROJ_VERSION=8.2.1
    export PROJ_DIR=${WASM_LIBRARY_DIR}
    export PROJ_INCDIR=${WASM_LIBRARY_DIR}/include
    export PROJ_LIBDIR=${WASM_LIBRARY_DIR}/lib
    export PROJ_WHEEL=1
    mkdir -p pyproj/proj_dir/share
    cp -r ${WASM_LIBRARY_DIR}/share/proj pyproj/proj_dir/share
test:
  imports:
    - pyproj

about:
  home: https://github.com/pyproj4/pyproj
  PyPI: https://pypi.org/project/pyproj/
  summary:
    Python interface to PROJ (cartographic projections and coordinate transformations
    library)
  license: "License :: OSI Approved :: MIT License"

package:
  name: pyproj
  version: 3.4.1
  top-level:
    - pyproj
source:
  url: https://files.pythonhosted.org/packages/c0/fc/fd53e45d2ad5862d32ab8614e70c3c1f52a8e0d8bd243ee6a23b6a481b4a/pyproj-3.4.1.tar.gz
  sha256: 261eb29b1d55b1eb7f336127344d9b31284d950a9446d1e0d1c2411f7dd8e3ac

requirements:
  host:
    - libproj
  run:
    - certifi
    - sqlite3

build:
  script: |
    export PROJ_VERSION=8.2.1
    export PROJ_DIR=${WASM_LIBRARY_DIR}
    export PROJ_INCDIR=${WASM_LIBRARY_DIR}/include
    export PROJ_LIBDIR=${WASM_LIBRARY_DIR}/lib
    export PROJ_WHEEL=1
    mkdir -p pyproj/proj_dir/share
    cp -r ${WASM_LIBRARY_DIR}/share/proj pyproj/proj_dir/share
test:
  imports:
    - pyproj

about:
  home: https://github.com/pyproj4/pyproj
  PyPI: https://pypi.org/project/pyproj/
  summary:
    Python interface to PROJ (cartographic projections and coordinate transformations
    library)
  license: "License :: OSI Approved :: MIT License"
