Cannot delete user if there are high amount of subscribers.

[dmatriccino]

When there are a lot of users subscribed to the blog, it's impossible to delete a user through wp-admin. For example,
if there are 400,000 users, and a user needs to be deleted for any reason, the page where it asks to attribute it's posts to another user, will try creating a dropdown of 400,000 options and stops rendering, which in turn does not allow you to continue to delete the user.

It might be better to just have the drop down consist of admin/contributers/authors instead of everyone.

[SergeyBiryukov]

Duplicate of #19867.