Revert "Fix a header file in python, so that #include <python3.9/Python.h> works."

This reverts commit 2772bb9c30.

Python maintainers rejects the proposed fix in
https://bugs.python.org/issue39026.  We'll need to make a correct fix,
or patch the downstream packages instead.

chapter01/changelog.xml

@@ -43,6 +43,16 @@
     appropriate for the entry or if needed the entire day's listitem.
     -->
 
+    <listitem>
+      <para>2021-04-22</para>
+      <itemizedlist>
+        <listitem>
+          <para>[xry111] - Revert 2772bb9c, as the proposed fix in it is
+          rejected by Python maintainers explicitly.</para>
+        </listitem>
+      </itemizedlist>
+    </listitem>
+
     <listitem>
       <para>2021-04-06</para>
       <itemizedlist>

chapter08/python.xml

@@ -42,10 +42,6 @@
   <sect2 role="installation">
     <title>Installation of Python 3</title>
 
-    <para>First, a header file needs to be fixed:</para>
-
-<screen><userinput remap="pre">sed 's|cpython/||' -i Include/cpython/pystate.h</userinput></screen>
-
     <para>Prepare Python for compilation:</para>
 
 <screen><userinput remap="configure">./configure --prefix=/usr       \