Remove almost all unpaired backticks in docstrings (#119231)

As reported in #117847 and #115366, an unpaired backtick in a docstring
tends to confuse e.g. Sphinx running on subclasses of standard library
objects, and the typographic style of using a backtick as an opening
quote is no longer in favor. Convert almost all uses of the form

    The variable `foo' should do xyz

to

    The variable 'foo' should do xyz

and also fix up miscellaneous other unpaired backticks (extraneous /
missing characters).

No functional change is intended here other than in human-readable
docstrings.

Lib/configparser.py

@@ -957,7 +957,7 @@ class RawConfigParser(MutableMapping):
                                 self._sections[section].items(), d)
 
     def _write_section(self, fp, section_name, section_items, delimiter, unnamed=False):
-        """Write a single section to the specified `fp'."""
+        """Write a single section to the specified 'fp'."""
         if not unnamed:
             fp.write("[{}]\n".format(section_name))
         for key, value in section_items: