Updating and improving clarity in help documentation for clean subcommands

[Autonymic]

This should close #2170.

I have removed the obsolete description about the traverse argument in the clean bots subcommand and fixed as well as added to the description of the clean regex subcommand.

I also improved the explanations for the message or timelimit argument and their relation to the channel argument across all clean subcommands.

[wookie184]

Thanks for doing this, I just have one comment.

[wookie184]

I think this bit is a bit wordier than it needs to be, I think something like this would suffice (note backticks can be escaped with \):

        The `regex` pattern must be enclosed in backticks (e.g. \`[0-9]\`). 
        If it contains a space it must also be enclosed in double quotes (e.g. "\`test [0-9]\`").

I'm not exactly sure what change the original issue was proposing to this part though. Thoughts?

[Autonymic]

The problem is that the intent seems to be to show how to write the regex part of the command, e.g. must be enclosed in backticks [0-9], but the problem is when it appears on discord it just turns into a code block due to the [0-9] being enclosed in ``, potentially making a less knowledgeable user confused.

When I tried escaping the standard backticks with backslash the linter didn't seem to like it, so I just chose to use special unicode characters that won't turn into a code block, even though it may cause confusion if a user tries to copypaste those backticks.

[wookie184]

Ah, in that case you can escape the backticks explicitly to make the linter happy

        The `regex` pattern must be enclosed in backticks (e.g. \\`[0-9]\\`).
        If it contains a space it must also be enclosed in double quotes (e.g. "\\`test [0-9]\\`").

(is the same as my screenshot above)

[Autonymic]

Yeah that seemed to do the trick, thanks! I removed some of the excessive words, so it should be a bit cleaner now.

[wookie184]

Looks good, thanks.

[ChrisLovering]

Looks good, thanks :)