Revert commit that was not a bugfix (#5301).

I won’t revert in 3.2, since Georg pulled this change in 3.2.2 and
released it.

Lib/mimetypes.py

@@ -432,7 +432,6 @@ def _default_mime_types():
         '.hdf'    : 'application/x-hdf',
         '.htm'    : 'text/html',
         '.html'   : 'text/html',
-        '.ico'    : 'image/vnd.microsoft.icon',
         '.ief'    : 'image/ief',
         '.jpe'    : 'image/jpeg',
         '.jpeg'   : 'image/jpeg',