Usernames are prefilled in autologout threshold field on the user edit page

Problem/Motivation

The autologout threshold field on the user edit page contains _user_ which indicates to some browsers a username could be prefilled (e.g. chrome).

Steps to reproduce

Use a browser that prefills fields and check the user edit page.

Proposed resolution

Remove the _user_ from the form field name.

Remaining tasks

User interface changes

API changes

Data model changes