[3.14] gh-115075: Fix info about initialization of mimetypes.MimeTypes attributes (GH-150691) (GH-156626)
They are no longer depended on the current value of global variables since
Python 3.9 (see gh-49213).
(cherry picked from commit 19363f20b6e014fd44c76f8a998b21845716e358)
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>