Add Delete action on Edit User screen

[mikemartin]

It's currently only possible to delete users from the User table view. This adds a lot of friction when you have thousands of users as you have to navigate through pages to delete the entry in the table.

It would be incredibly useful when editing a User in the CP to have a Delete Action in the actions dropdown alongside Edit Blueprint. See screenshot.

[jasonvarga]

Will be covered by https://github.com/statamic/cms/pull/6375