FIX: Error messages from editing user being swallowed (PR #10908)

The format of the error responses is different than what the code is expecting. This was causing error messages to be ignored. Here is an example of the correct format being used. https://github.com/discourse/discourse/blob/6e2be3e60bb882dd92d270d11c71fba9b0901b5e/app/assets/javascripts/discourse/app/controllers/preferences/email.js#L103

Screenshot 2020-10-13 100610

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