bpo-37529: delete duplicate mimetype for bmp files

[akulakov]

This is in effect a backport of #26300 to 3.9 .

I'm not sure I'm doing this right, this is the first time I'm doing a backport. (but the change is one deleted line so it's probably the easiest way?)

Not adding news entry because #26300 didn't have one.

https://bugs.python.org/issue37529

[Fidget-Spinner]

There's a guide to backports and the correct format here: https://devguide.python.org/gitbootcamp/#backporting-merged-changes.

Also one part it doesn't mention, please prepend the target branch version in your PR title. So in this case it's [3.9] bpo-xxx Remove duplicate mime type mapping .bmp -> image/x-ms-bmp.

Otherwise, this all looks good to me. Thanks.

[serhiy-storchaka]

#26300 was not backported. Instead of creating a separate PR manually we just add labels "backport to X.Y".

[Fidget-Spinner]

Andrei doesn't have permissions to add labels yet. So I'll add it for him.

Edit: Nevermind woops, it seems that Serhiy has already set the label. Thank you Serhiy :).

[Fidget-Spinner]

It seems that we're not going to backport this since it's a potentially backwards incompatible change in a minor version update. Please see https://bugs.python.org/issue22589 for the discussion @akulakov on something similar in the past . Thanks.