[cleanup] Remove unused idlelib.editor._sphinx_version()

The `_sphinx_version()` function is no longer needed since CHM
(Compiled HTML Help) documentation files are no longer installed.
This removes the dead code as indicated by the TODO comment.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: gpshead

Lib/idlelib/editor.py

@@ -35,18 +35,6 @@
 TK_TABWIDTH_DEFAULT = 8
 darwin = sys.platform == 'darwin'
 
-def _sphinx_version():
-    "Format sys.version_info to produce the Sphinx version string used to install the chm docs"
-    major, minor, micro, level, serial = sys.version_info
-    # TODO remove unneeded function since .chm no longer installed
-    release = f'{major}{minor}'
-    release += f'{micro}'
-    if level == 'candidate':
-        release += f'rc{serial}'
-    elif level != 'final':
-        release += f'{level[0]}{serial}'
-    return release
-
 
 class EditorWindow:
     from idlelib.percolator import Percolator