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- [x] Add new / update outdated documentation

From 46026c40dc86c78c938da66e6671ed0d792d71c9 Mon Sep 17 00:00:00 2001
From: Hood Chatham <roberthoodchatham@gmail.com>
Date: Sun, 26 Dec 2021 07:34:40 -0800
Subject: [PATCH 08/13] Rename _page_trend_test.py to prevent test unvendoring

unvendor_tests will unvendor any file that ends in _test.py.
Prevent that by changing the name of this file.
---
 scipy/stats/__init__.py                                   | 2 +-
 scipy/stats/{_page_trend_test.py => _page_trend_test_.py} | 0
 scipy/stats/meson.build                                   | 2 +-
 3 files changed, 2 insertions(+), 2 deletions(-)
 rename scipy/stats/{_page_trend_test.py => _page_trend_test_.py} (100%)

diff --git a/scipy/stats/__init__.py b/scipy/stats/__init__.py
index 70a527849..8ce1ae379 100644
--- a/scipy/stats/__init__.py
+++ b/scipy/stats/__init__.py
@@ -480,7 +480,7 @@ from ._resampling import bootstrap, monte_carlo_test, permutation_test
 from ._entropy import *
 from ._hypotests import *
 from ._rvs_sampling import rvs_ratio_uniforms, NumericalInverseHermite
-from ._page_trend_test import page_trend_test
+from ._page_trend_test_ import page_trend_test
 from ._mannwhitneyu import mannwhitneyu
 from ._fit import fit
 
diff --git a/scipy/stats/_page_trend_test.py b/scipy/stats/_page_trend_test_.py
similarity index 100%
rename from scipy/stats/_page_trend_test.py
rename to scipy/stats/_page_trend_test_.py
diff --git a/scipy/stats/meson.build b/scipy/stats/meson.build
index dfac9e073..3c5cc673f 100644
--- a/scipy/stats/meson.build
+++ b/scipy/stats/meson.build
@@ -192,7 +192,7 @@ py3.install_sources([
     '_mstats_basic.py',
     '_mstats_extras.py',
     '_multivariate.py',
-    '_page_trend_test.py',
+    '_page_trend_test_.py',
     '_qmc.py',
     '_relative_risk.py',
     '_resampling.py',
-- 
2.25.1


From 46026c40dc86c78c938da66e6671ed0d792d71c9 Mon Sep 17 00:00:00 2001
From: Hood Chatham <roberthoodchatham@gmail.com>
Date: Sun, 26 Dec 2021 07:34:40 -0800
Subject: [PATCH 08/13] Rename _page_trend_test.py to prevent test unvendoring

unvendor_tests will unvendor any file that ends in _test.py.
Prevent that by changing the name of this file.
---
 scipy/stats/__init__.py                                   | 2 +-
 scipy/stats/{_page_trend_test.py => _page_trend_test_.py} | 0
 scipy/stats/meson.build                                   | 2 +-
 3 files changed, 2 insertions(+), 2 deletions(-)
 rename scipy/stats/{_page_trend_test.py => _page_trend_test_.py} (100%)

diff --git a/scipy/stats/__init__.py b/scipy/stats/__init__.py
index 70a527849..8ce1ae379 100644
--- a/scipy/stats/__init__.py
+++ b/scipy/stats/__init__.py
@@ -480,7 +480,7 @@ from ._resampling import bootstrap, monte_carlo_test, permutation_test
 from ._entropy import *
 from ._hypotests import *
 from ._rvs_sampling import rvs_ratio_uniforms, NumericalInverseHermite
-from ._page_trend_test import page_trend_test
+from ._page_trend_test_ import page_trend_test
 from ._mannwhitneyu import mannwhitneyu
 from ._fit import fit
 
diff --git a/scipy/stats/_page_trend_test.py b/scipy/stats/_page_trend_test_.py
similarity index 100%
rename from scipy/stats/_page_trend_test.py
rename to scipy/stats/_page_trend_test_.py
diff --git a/scipy/stats/meson.build b/scipy/stats/meson.build
index dfac9e073..3c5cc673f 100644
--- a/scipy/stats/meson.build
+++ b/scipy/stats/meson.build
@@ -192,7 +192,7 @@ py3.install_sources([
     '_mstats_basic.py',
     '_mstats_extras.py',
     '_multivariate.py',
-    '_page_trend_test.py',
+    '_page_trend_test_.py',
     '_qmc.py',
     '_relative_risk.py',
     '_resampling.py',
-- 
2.25.1

