The design of DefaultShowFullName has some problems, which make the UI
inconsistent, see the new comment in code
This PR does a clean up for various legacy problems, and clarify some
"user name display" behaviors.
---------
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
The first step of #23328
This PR cleans:
1. Dead function like `SubStr`
2. Unnecessary function like `UseHTTPS`, it should be provided by
`window.origin`
3. Duplicate function like `IsShowFullName`, there was already a
`DeafultShowFullName`
I have searched these removed functions globally, no use in code.