docs: remove duplicate entries for bot.{name,nick,user}

[dgw]

Description

Sphinx 3 started complaining about duplicate object descriptions. I'm too lazy to keep updating my local Sphinx (was still on 1.8.x until today), but I spotted the warnings in Netlify site build logs.

Resolves these warnings (taken from the sopel-irc/sopel.chat#29 merge build on Netlify):

6:45:58 AM: /opt/build/repo/_sopel/sopel/bot.py:docstring of sopel.bot.Sopel.name:1:
WARNING: duplicate object description of sopel.bot.Sopel.name, other instance in bot,
use :noindex: for one of them
6:45:58 AM: /opt/build/repo/_sopel/sopel/bot.py:docstring of sopel.bot.Sopel.nick:1:
WARNING: duplicate object description of sopel.bot.Sopel.nick, other instance in bot,
use :noindex: for one of them
6:45:58 AM: /opt/build/repo/_sopel/sopel/bot.py:docstring of sopel.bot.Sopel.user:1:
WARNING: duplicate object description of sopel.bot.Sopel.user, other instance in bot,
use :noindex: for one of them

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make quality and make test)
• I have tested the functionality of the things this change touches

Notes

This commit can be cherry-picked to the 7.0.x maintenance branch just in case we actually release another patch version, but I don't think anything is actually broken because of this. The definitions in docs/source/bot.rst just make these three properties appear at the top of the built HTML page, instead of in alphabetical order with the rest of the things. (The duplicate rST defs came from b567c72, over four years ago. I think we're past needing them.)