Refactor sandbox hints (#2218)
* Clean up comments
* Stop using deprecated `GetConVarNumber`
* Use string.gsub's function mode for binding lookups
```
Lua 5.1.5 Copyright (C) 1994-2012 Lua.org, PUC-Rio
> text = "foo %+one% bar %+two% baz %+three%"
> function replacer(res)
print("replacer!", res)
return string.upper(res)
end
> print(string.gsub(text, "%%([^%%]+)%%", replacer))
replacer! +one
replacer! +two
replacer! +three
foo +ONE bar +TWO baz +THREE 3
```
* Formatting
* Update cl_hints.lua
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Co-authored-by: Rubat <3299036+robotboy655@users.noreply.github.com>
